Make it into an HT.

I'm offended that y'all are calling it a dash!
Clearly this is an UNDERSCORE_Duh!

IC-706, FT-857D etc...

MFJ has a new telescopic 17' portable vertical with base loading coil, counterpoise wires and a simple mount for about $100.

Possible power line noise.
Get a portable RX and walk under the lines until the signal peaks.
Use binoculars/telescope to search for visible damage to insulators and transformers.

This will allow a straight run of LMR400 from roof to amp:

http://store.rlham.com/shop/catalog/product_info.php?products_id=68864

or

http://antennasystems.com/product/larsen/NMO38THK.html

Also, it only requires a 3/8" hole so that makes things easier.
Yes, the roof is a WAY better choice for an antenna.

At 2m (VHF) the loss of RG58 vs. LMR400 is negligible for that short of a run.
Once you go to 70cm (UHF) and above, the loss starts to climb in the smaller coax sizes.
RG174 is the worst at UHF and the power rating is also low.

Alan K0BG is a frequent poster to the forums and his site is:
www.k0bg.com

It would be wise to give it a long look.
I built my mobile setup based on his info.
Even though he would most likely balk at my mobile, it is quite the performer and fills my needs very well.
You get what you pay for and frankly, there is no substitute for a solid and well thought out install.

I think you answered your own question.
Any (extra) connection is going to add some loss.
You would most likely have more loss in the RG58 pig tail than in the barrel connector.

If you really want to run that much power mobile, consider a different mount location i.e. the roof.
The roof will act as a "faraday cage" to "help" protect yourself and passengers from the high levels of RF radiation.

With such a long antenna, you can expect to have some damage to the trunk lip as the wind loading will cause lots of strain.
If you were to use a standard NMO with a 5/8" hole drilled in your roof, you would want a sheet metal backing plate.
This can be found at Lowes/Home Depot in the hardware section. A 1' x 1' 20ga sheet should work.
Drill a matching 5/8" hole in the center, bend the metal to the same contour of the roof and apply some adhesive.

This will also allow LMR400 for the full length from radio to antenna.

BTW, your antenna is only rated to 150W. Giving you a useful power input at the feed point of only 75w!
Always double the power factor to make sure your system can handle a long key down.

The cheapest method is to build a "trombone" capacitor and drive it with a stepper motor.
I think elecraft has a write up in the tech notes about this.
AD5X dot COM has info on sending a DC control voltage through your coax.
I used some clear flexible tubing for the dielectric.
My loop is a 4' octagon and tunes down to 20m.

73, Damon

Of those, i'd choose Elecraft. :-)

Otherwise, the FT-450 has the best bang for buck features.

Nah, I use mine for occasional luggage and flood lights for playing in the woods.

Having said that, it's a good idea but it just won't work. Good on you for giving some thought to different antenna possibilities.
You can use the rack as a foundation to mount taller insulating supports to run a wire loop.
This is referenced in the (free to download from SGC) SSB Users Guide.
I believe they cite a minimum 18" spacing from the roof.

You could use some painted 1/4" fiberglass tent poles for stand-offs.
It might look a little silly. But then, so does my 102" whip with cap hat.

The Xterra is a good looking vehicle and a well mounted (and thought out) HF vertical antenna install will not take away from its looks.
I'm planning an install into a Jeep Cherokee Sport and if anything, I think an HF antenna makes it look tougher!

Mine is off by 1/2", bugs the heck out of me... Still works fantastic.

Worthless, just box it up and send it to me.
That way you'll never have to worry about it.

MFJ-10-10989D $29.95.

I had two 6BTV's over the years and had good results.
Here at my new QTH, I decided to go stealth and came up with a cheap working setup.
My most heavily used radio is my K2/10. I have others but don't need 100w.

After being a huge skeptic of the 43' fad, I decided to do a little research on them.
I couldn't justify $300+ for some silly simple antenna that couldn't possibly work so I used some wire to try it out first.
A trip to Lowes got me a 500' roll of 14AWG and some 1/8" rope thimbles (tear drop shaped loop protectors).
I was given an 800' roll of RG-6 75ohm coax and all that I needed now was a plastic 4"x4"x3" electrical junction box with RF connections.
In side the box is an MFJ-10-10989D terminated with an SO-239 on the input and two 5-way binding posts for the vertical wire and radials.

Total cost was about $60 to $75. I shot an arrow with spiderwire into a very tall pine tree.
This was used to pull my 1/4" rope and wire vertical.

What have I learned about the 43' antenna fad? If you have tall trees, why spend $300. Also, they do work!
I used the remaining wire for radials. The UNUN makes this antenna DC grounded by default so it is very quiet on RX.
You should have a horizontal antenna to switch to if possible to help "fill in the gaps". (this is for ANY vertical)
Without base loading inductance, expect good 60-10m performance. I do make contacts on 80m with a good bit of loss.
10-15w SSB and 5-8w DATA has netted me contacts world wide.
The best part, no one knows it's there!

go to www.ad5x.com for some good info including RG-6/PL-259 soldering.

73, Damon