I'll just throw it out there as a wild idea, but what about AlBeMet  (it's a funky aluminum beryllium composite).. higher thermal conductivity than aluminum. Has a CTE that's pretty close to ceramics, Toxic as all get out if machined, but hey, maybe it might be a solution.

A couple possible answers spring to mind:
To improve the regulation by swamping the varying load from the amp?
Because one of those resistors per capacitor could go open?

The last is actually unlikely. And, in any case, if that WERE the case, the system is still unsafe, even with a bleeder across the stack, because it won't always discharge everything (consider a trivial example of 2 caps, 10uF each, charged to 450V and -450V respectively, in series)

Oooh.. face milling or grinding or lapping copper.  that's a chore and not as easy as, say, aluminum or steel.  Talk to your machinist before you chose that approach.

What about cutoffs from a big billet or bar? 

How much thermal conductivity do you need?  Yeah copper is almost as good as silver but only about twice as good as aluminum.   Folks use copper. but I'm not sure it's actually needed, it might just be convenient because it's solderable, it's cheaper than gold or silver, and it's soft enough that you can squish something harder down on it and make good thermal contact.
Is the "spreading" the important thing (would a thin copper layer over an aluminum substrate work?  Yes, there's all kinds of CTE mismatch issues to deal with but maybe they'd be easier.  You can use explosive bonding or diffusion bonding for instance. )

or what about using a thermal transfer medium/gasket (grafoil, Chotherm, NuSil). (I'm not wild about those, but they might get you where you need to go.)

I think, though, that this discussion points up that designing a high power  low IMD amp is more a mechanical and thermal engineering problem than an electrical one.

Even without efficiency limits, it's a challenge.  20% efficiency in Class A with very good IMD over multiple octaves isn't easy.

Yeah, and rigs like the IC7000 aren't really set up well for repeater/echolink/irlp kind of ops where you need touchtones etc.

That said, it works just fine, and if you have limited dash space (and you don't want pictures of your car gracing hamsexy.com), it's a compromise.

(OTOH, I think it would be cool if someone would make a mobile oriented version of something like HRD that runs on an iPad that you can mount on the dash)

If you're talking about a difference in distance of a few feet, it doesn't make any difference.

But I'm not sure about whether you can make that bonding connection *inside* your breaker box.

It's pretty easy to punch a hole through stucco or drywall and put a nice looking cover over it so that it looks like it is supposed to be there.  You want what's called a "mud ring" or "old work" frame.  It's like an electrical box with no back and short sides, but has the screw holes to mount a standard cover plate on it.  You carefully cut a hole in the drywall with a suitable saw (or serrated bread knife) that is exactly the size of the outside of the oldwork box.  You put the thing through the hole, and there's a couple screw actuated lugs that "clamp" against the backside of the drywall.  Do you work, put a duplex or triplex coverplate on, and you're done.

The usual guideline is that you want the voltage to be <50V after some reasonable time. Reasonable is usually determined by how long it takes to get access to the HV parts.  If you have to remove 17 screws using 3 different screwdrivers, you can have a longer time than if it's flip a latch and open the cover. 

From 2kV to 50V is about 3.7 time constants  (ln(2000/50)), so if your RC time constant were 10 seconds, after 40 seconds, the system is "safe".

For systems where you want a long time constant (to save power dissipation in the bleeder) and where the door isn't opened much (e.g. you rarely take the covers off, but you want the thing to be safe within a reasonable time after turning off the switch) one strategy is to have a "automatic" mechanical shorting bar on the HV.  Normally, you turn off the power, wait a minute, then open the door.  But if somebody forgets to wait, or whatever, and open's the door, the shorting bar dumps the charge (with a bang and a flash, usually.)  Yeah, you might need to fix some broken parts, but at least nobody is dead.

Unless done very carefully, this approach is unsafe. If the relay sticks, you've lost the safety function of the bleeder.  What you might consider is a slow (high value R) that's permanently across the C, and the switched low value R to quickly discharge the C.
You want to have some resistance in that shorting stick, to limit the current to something like 10Amps.  Big bangs and rapid discharge is very hard on the capacitors (and your nerves, and little pieces of molten metal flying about are just not a great thing)

Unlike hams, though, commercial and military users are willing to pay more, which can cover the cost of test/characterization either at the semiconductor mfr or the radio mfr, and they can buy in sufficient quantity to mitigate some of the process variation issues. (although.. it's nothing like 30 years ago, where running 883B lines, etc. was a big fraction of the sales.)
Actually, not so much VCs (who are willing to bet on a huge return), but more downstream investors on a larger scale who are looking for small incremental changes.  Can you reduce cost by 5% kind of things?  Deming (among others) has bad things to say about cost accounting and control as  management philosophy.  Fine if you're running an established product on an assembly line, not so good for new technology development.

Oh, I think if you were sitting the monitoring van out front, I think you can get a pretty unambiguous measurement without worrying about propagation effects.

Performance measured how?
The inexpensive Ameritron tube amps have manual plate tuning controls and very little internal protective circuitry, if any, which works on a tube in the hands of a human operator who will make mistakes, but would almost certainly result in instant death for RF transistors when mistuned.  So SS amps use broadband designs and output filters.

What has to change?
The market for amplifiers. As you pointed out, you expect to use your tube amp til you die, so you're not a customer for a SS amp.  And I suspect you are typical of much of the potential market. 

Eventually, new hams will come into the market, want an amplifier, not be interested in tubes, buy a SS amp as currently constituted, complain about the performance(measured however), and the mfrs will respond with new products.  No/Auto tune amps are a lot easier to use, and I don't think the somewhat arcane and esoteric skill of tuning up a tube amp brings a lot to the operator. The reason they dominate now is that there's a lot of manually tuned amps in existence, and they're cheap, not because people love to turn the knobs.  It's not like manual vs automatic transmission, where there is some benefit from the manual transmission.  Given a choice between a top of the line autotune tube or no-tune SS amp and a low end manual everything, I'll bet most hams would choose the former (hmm, look at those contest stations and the DXpeditions... They love them their big Alphas)

If you're selling the part into a market which doesn't care about IMD, then why would you bother characterizing and publishing the data.  Surely not to just satisfy the curiosity of a casual observer.

This is why amplifier design isn't cookbook. The data sheet only lets you identify candidate parts, then you get to buy samples, and test them for what you really care about.

If you're smart, you'll get multiple parts from multiple lots to characterize the spread.

And pray that the mfr doesn't change the process, or that your parameter of interest happens to be tied to something that they DO care about.

And, if you want the manufacturer to guarantee performance on some new parameter, you can pay for it separately (which is what makes MIL and Space parts expensive..)   radiation tolerance is a good example of something that can change radically with small changes in process.

I have a 7000 in my car and I like it.  I think you should take the damage reports with a grain of salt.. there's thousands of radios in the field, but only people who have problems bother to report it, so the actual incidence of problems is pretty low.  I have a coworker who had problems with is 7000, but it's been fixed.

One thing for ALL mobile rigs: they need cooling air.  Tiny radio, lots of heat in a small space. Don't go shoving it under the seat with the dustbunnies and candy wrappers or into the stock radio spot in the dash.   I have my radio in the trunk mounted on the side wall where it won't get covered up by stuff and just the faceplate up front.

I don't know (not having a 7200), but I would think that if you like the 7200's user interface and operating modes, then another radio from the same company might be easier to use.

That's sort of true.  The loop needs to be big enough.  And if it's outside, you need to bond things (coax shield) to your house's electrical safety ground.  But you don't need an "RF ground"

But then, you wouldn't need one for any sort of dipole looking thing, either.  You only need an RF ground if you're building a vertical (or something that looks like a vertical, such as a L or flattop)

You don't need to cut the concrete away.  Somewhere below the entrance box (inside the wall), there is a wire coming up from the foundation to provide the grounding connection. You need to hook your bonding wire to that wire.  It's punch a hole in the wall time (unless there happens to be somewhere accessible.  In my house (SoCal late 90s), all the conduits for power, telephone and cable TV comes up in the same 16" space between the studs, and there's a grounding wire right next to the conduits, all of which is accessible behind the Cable TV access panel (which is about a foot wide and 6" high).  the power conduit has no breaks and goes right into the meter box (so you can't get access to the feeders), but the other conduits just end, and the cables come out.

There probably is no ground rod anywhere in your system (unless some less than competent cable TV or Satellite installer drove one because they couldn't find the right grounding connection)