I elected to core my 12" thick poured concrete walls.  Here's what it looks like from the outside.  Note the ground wire coming in from my tower and headed back underground to the utility ground rod farther to the right of this picture. Along with the Heliax and coax, there are rotator control cables, SteppIR control cables for the vertical and yagi, and a DC supply cable for my weather station's heated rain bucket so I can obtain water equivalent readings from snowfall.
http://i9.photobucket.com/albums/a96/TwoSevenRight/71e5dcb0.jpg

This is from the other side of the hole.  Note home clean the edges are with little breakout of concrete.  Inside the hole on the back of the plate are where my Polyphasers are mounted out of the weather.  I stuff a rag in the hole for weak insulation.  The concrete coring contractor charged me $300 for the job, and left the core in case I or some other owner of the house would want to seal the hole up some day.
http://i9.photobucket.com/albums/a96/TwoSevenRight/P1020459.jpg

If you give yourself 20 minutes, you should be able to get a seat in most of the forums.  Hint...Late Friday afternoon is great for inside shopping.  Saturday is crazy inside, especially if the weather outside is bad.  Do not take big purchases with you, or you will be subject to OH sales tax.  Instead, order the item and have it shipped to you home.  Your card will be charged off site, and free of sales tax.  Many smaller purchases will have a "tax included" flat price, and of course tailgaters are tax exempt.  See you there!

The need to arrive early varies from forum to forum.  But two yearly presentations, Antennas, and the DX forums get big attendances.  Also consider that rooms may have a preceding forum going on so even if you get there early, you'll most likely need to wait in the hallway.

You're going to have fun.  Bring money!

An American Beauty with the proper width tip that fits in the groove of the PL-259 body is hard to beat.

The 1000 was my at the top on my Dayton shopping list several years back, so my the data which forms my opinion is a few years old.  Nicely made with a great tube.  If you don't abuse it, the GU74B may last for many years. It covers 160-6 meters which is rare.  I was sold.  HOWEVER... I was turned off by the the sales team at Dayton which featured the owner K1LZ and his (at the time) US sales rep. So I moved onto the Emtron booth and received a warm welcome from their US rep and owner Rudi who pulled the covers off their DX1d, an amp which featured the same GU74B tube but which didn't have the 6m option.  That was a negative.  But I liked the sales force was friendly and willing to answers any questions.  The amp was beautifully constructed with a rugged chassis and transformer.  Is it unreasonalble to expect to be treated at least cordially when you've got a roll of $3500 in your pocket to drop on a hobby?  I didn't think so.  I went with the Emtron.

I guess if you buy from a distributor, you won't encounter personalities that make you form a general opinion of the product.  But at the time, neither amp was sold by a retail outlet (Emtron still isn't) so you were forced to seek out the individual that represented them in the US.

Attic entry concerns me for safety reasons.  It's a path through a relatively inaccessable part of your home for lightning.  Transmission line could routed across flammables, and may be possibly routed down through an interior wall to your operating position.  I believe that your transmission lines should be visible from the point of entry to your gear.

At the risk of repeating myself.....ah what the heck:
The ARRL lab measured 3rd order IM products on TX of -22dB on 40m @ full output (5W).  If you take the output of the 1500 and boost it 13 dB by running it into an amplifier, any amplifier, you will end up with spurs of considerable power inside the operating band.  That example is assuming the amplifier doesn't introduce any IMD of its own, and if you can show me one of those, I'll buy it.  The laws of physics are irrefutable: Even order IMD products typically fall outside the band and can/could be filtered out by a following PA.  Odd order IMD products typically fall inside the operating band and thus cannot be filtered out by any PA.

The is no amplifier...repeat NO amplifier commercial or home brew that is capable of filtering the 3rd order IMD products generated by the 1500 because they fall within the band you're operating in. If you drive a typical 100 watt amplifier with a Flex 1500, third order IMD can be down as little as-9db from your transmitted signal.

The Flex 1500 is an interesting QRP transceiver.  Let it remain that.

Let me offer a shortcut.  Once you determine the overal length of your wires. Get two wood stakes, and and pound them into the ground spacing them apart half the length of your radial length.  Take your spool of wire and fasten the free end to a screw or nail in one of the stakes.  Pay out the spool by walking 'round and 'round the stakes until the spool, or you is exhausted.  Cut each turn as it passes around the starting stake, and you've got radials of your deisre length.  Don't worry whether it's twisted pair or in a jacketed bundle.  Just strip and tie all the conductors in the bundle together at the ground point of the antenna.  While the majority of the radial in my field are insulated stranded 16AWG copper, I also have many hundreds of feet of hi-tensile aluminum electric fence wire.  While its lifespan is shorter than copper, they have lasted 4 years so far installed and pinned to the surface, although now mostly covered by field grass thatch.

Here's my radial "fixture": http://i9.photobucket.com/albums/a96/TwoSevenRight/cutting_radials.jpg

Elecraft K3 w/second receiver, P3 panadapter with the SVGA card driving a 24 monitor. 

When working splits, you can here DX calling in one ear, and the pileup in the other ear.
You can run diversity receive off of two antennas; maybe a high antenna, and a beverage.

Is there anything you can't do on HF with the K3?  I haven't encountered it yet.

Central MA to Philadelphia, PA to Dayton, OH and back is about 1600 miles.  That's how far I will travel to a hamfest this year..... but it's the Hamvention; world's largest hamfest in the world's crappiest location.  With three guys in the vehicle, gas, tolls, and lodging, etc. are down near the noise floor of the yearly "toy money" budget.

Michael, what I'm suggesting is this.  If you enjoy your 1500, by all means do so.  The transceiver is type accepted.  But without a spectrum analyzer, you have no way of knowing what your signal looks like with the exciter at any output level.  My suggestion is to have fun with your 1500, but do so barefoot until you can verify your spectral purity running with reduced exciter power.

As I mentioned earlier, I'd have cash in fist at the Dayton Flex booth this May if the 1500 wasn't so dirty on xmit.

Graphs aside for a moment, here's an example that even a novice should follow:
Suppose you're sitting on 14200kHz USB and you put a two tone test signal of 700Hz and 1900Hz into the transmitter.  You will get RF carriers at 14200700Hz and at 14201900Hz which is what you want.  Unfortunately due to any non-linearity in the 1500's transmitter you will get rich IM products.  The first set, called second order products, will occur at the sum and difference of the two carrier frequencies, 28402600Hz and 1200Hz.  Both of these are sufficiently removed in frequency from the desired signal that they can be attenuated by a simple bandpass filter tuned for the 20m band.  The second set of IM products, called third order products, will occur at 2f1-f2 and 2f2-f1 or 2*14200700 – 14201900 which equals 14,199,500Hz and 2*14201900 – 14200700 = 14,203,100Hz.  As you can see both of these signals fall within the 20m band so they cannot be filtered out.  It turns out that all even order IM products fall out of band if the band is less than one octave wide and all odd order products up to a limit fall in band.

This example uses simple tones but the transmitter must pass complex signals such as voice or PSK31 where we don’t know the precise frequencies in use at any one time so we can’t get clever and use narrow band notch filters to get rid of the inband products.

Users who state, "I've got (X number) of watts of clean power" must either A) Be bending the rules of physics, or B) Have no idea what they're dealing with.  Using the 1500 behind a 500W amplifer like the respected Elecraft amp will generate several watts of IM products in the band you're operating within; it's irrefutable.  I can can work the antipodes with several watts of power, so your spurs are capable of being heard world-wide.  In short it does not appear that the Flex 1500 will ever be a good exciter for a high power amplifier.  I wish it were...

The ARRL lab measured 3rd order IM products on TX of -22dB on 40m @ full output (5W).  If you take the output of the 1500 and boost it 20 dB by running it into an amplifier, any amplifier, you will end up with spurs of several watts inside the operating band.  That example is assuming the amplifier doesn't introduce any IMD of its own, and if you can show me one of those, I'll buy it.  The laws of physics are irrefutable: Even order IMD products typically fall outside the band and can/could be filtered out by a following PA.  Odd order IMD products typically fall inside the operating band and thus cannot be filtered out by any PA.  So for me, the Flex 1500 remains an interesting QRP setup.  I've operated my firend's and I love it.  I'd buy one in a second.  But I already have two QRP transceivers, and no responsible amateur who knows and understands the facts would place any amplifier downstream of the 1500's output.

Another item of great importance:  If the control head is separated from the radio, you must install the small metric screw to secure the connetor to the control head body.

Another thing that helped for me was to attach a short ground braid from the ground screw on the 7000 to the nearest ground point on the vehicle's body.

What year Tahoe, Dave?  I don't want to hijack the thread. Mind if I conact you offline?