I wonder if they've revived the M series gun trucks, or ever will. That would be an intresting throwback.
They were total "home made" jobs, (
http://www.guntrucks.com/SlideShow/ ) but it would probably work if constructed to meet todays requirements. A duece and a half or a 5 ton can support alot of weight, you have alot of room to work with, so you could armor the piss out of them. Espeically the floors.