Truck gun.

I just started working with a Brocock Concept XR Lite as a review gun. Preliminary thoughts are that the gun is built like a brick! It's got an aluminum chassis and just seems stout. AR looking gun and fairly compact. I think there's an option with a folding butt stock for it to get even shorter. The build just seems utilitarian, especially for a gun that's gonna get knocked around in a truck. They come in .25 for your higher power needs. Seems like it would meet a lot of your specifications. I've not shot it much but my initial impression of it makes me think it could be worth considering for your desired use. 
 
Anything 2nd hand Edgun really, solid enough to be bounced around and keep on working. Would prefer a R3 22/25 singleshot std. Always works, solid and simple. Should not be expensive to buy now. Edgun Veles, Lelya and Leshy work too, but would be more expensive, difficult to get hold of or less powerfull.

Difficult to get hold of? Less powerful? Does not compute... My Lelya for example was slinging .22 polymags at over 1000 fps. I actually eased up on the hammer spring adjuster a good amount when going to the Hades. It was shooting them slightly faster then the polys. Knocked them down to 946fps. Stock regulator is at 125 bar.

My Leshiy is currently shooting the .177 JSB monsters 13.43 grains at 844fps with the short 250mm barrel. Stock regulator un-adjusted. This was a .22 Leshiy that I dropped a .177 barrel in. Hell, it was shooting the .177 polys at 1014fps.