Desktop in the truck?

If you do it there is one thing that I would do, that would raise your price a good bit but make it so the computer would live longer.
I would get a solidstate hard drive.
Your biggest issue will be hard drive damage due to vibration and bouncing of the truck. You can isolate some like you said, but not enough.
Also, if you are using a dedicated graphics card you will really need to keep an eye on it, they do not take allot of bouncing before they work loose.

 

A dedicated graphics card is built right into the main board, so no worries of that coming loose. If you had a AGP or PCIE graphics card then that is another story, these cards go in their own slot, and may come loose over time. I'm not to sure how a desktop HD will take the bumps, your idea of using rubber isolators sounds like a good idea. One thing you do want to mind is the CPU fan and heatsink, if it is a OEM from say AMD or Intel, it uses four pegs that snap into the motherboard. This is fine for sitting on a desk, but a lot of bumps and it could come loose or even fall off, causing your CPU to overheat. You may want to look into a aftermarket Fan and heatsink that actually have a motherboard back-plate, which the heatsinks 2-4 connectors screw into. Make sure also that the computer has good airflow, poor airflow will cause the components to overheat.

Check out this page for a example, and notice the mounting hardware:
http://www.newegg.com/Product/Product.aspx?Item=N82E16835118223

 

?? Top heavy? What the heck is that supposed to mean? lol I can safely say I've never had a computer become top heavy from installing an aftermarket heatsink.

The Zalman that he listed is one of the best heatsinks on the market, and easily cheaper than even a single component of a water cooling system.

How much are you looking to spend on this thing? With a water cooler, radiator, lines, distro blocks/joints, cooler blocks, etc. you are easily going to match the cost of a decent gaming laptop.

 

yep, by the time you get to the water cooling and the cost of everything and building it, you will find that you will spend more than what you can get a laptop for.
and top heavy towers, the only thing at the top is the power supply. the cpu heatsink and fan will be in the middle of the tower so that would not make it top heavy. the heatsinks are not heavy.

 

Liquid cooling will cost you a pretty penny to get a decent setup. You dont want to buy any old liquid cooling setup, remember if you develop a leak your system is toast!! The Zalman is one of the best aftermarket coolers around, and far from being heavy. It has a very secure mounting system, and you wont have to worry about a hose or waterblock springing a leak.

Here is another suggestion from Zalman, this one sits flat compared to the 1st one I linked you to, which may be better especially if you have a smaller case.

http://www.newegg.com/Product/Product.aspx?Item=N82E16835118030

 

The case I have is the Antec 902, it has 2 120mm fans in front, 1 120mm fan in back, and a 200m fan on top, and the PSU sits on the bottom.......................Excellent case!! The cooling is 2nd to none, and I need it for the high end hardware I run.
http://www.antec.com/Believe_it/product.php?id=NzIy
As far as XFX motherboards, never used them. Right now Gigabyte Ultra Durable boards are one of the best you can buy, if not the best. I currently have a Gigabyte GA-P35-DS3L, excellent board. Overclocks well and is rock solid!!

My current specs are:
Gigabyte GA-P35-DS3L
Intel Quad Q6600 overclocked to 3GHZ/Cooled by XigmaTek HDT S2183
4GB Crucial Ballistix Memory
EVGA GTX 280 SSC Edition
LG Flatron 22 Inch LCD
XFI Extreme Music Sound Card
640 GB Western Digital Caviar SE16 Blue
Antec Quartto True Power 850 Watt
Antec Nine Hundred and Two Case
Windows Vista 64bit