It has been done, before... By GM Racing...
https://www.facebook.com/chadragland/me ... c8778989e4http://www.thefreelibrary.com/Vortec-Po ... a062542914It's a mid-engine with a custom cast 5.0l I6 race block making 650hp at 7500rpm, and I'm sure it's still over 3000lbs, even with a custom carbon fiber body. I can't find a weight on this one in particular, but the class of SCORE unlimited trophy trucks that this competed in usually weigh around 6000lbs, race-ready. I know that the lightest every trophy truck was fielded by BMW, and it weighs in at 4500lbs, and is substantially smaller than the rest of them, the TB included. The lightest one before that was about 5380lbs, from what I gather.
However, some light reading for you on your weight spec:
http://www.fourwheeler.com/features/tro ... hnology-2/"They probably don’t realize that weight does have its place in Trophy-Truck racing. Nothing can bomb through the rough like a Trophy-Truck and part of that is actually due to its extra mass. Lighter vehicles tend to deflect or skip (somewhat) over the rough while heavier TTs simply absorb it. The experience is similar to doing a trail on an uber-lightweight mountain bike and then doing that same trail on a dirt bike. Compared to the moto, the mountain bike will always feel more “active,” deflecting off bumps where the moto will blow right through them. Because of this, many builders were not exactly looking to shed some pounds."
Based on your questions and answers, I think you've got a hell of a lot of learning to do about desert racing, before you even look at building anything.
Mike