I think the campaign would need to be Civilian Trucks.
Here's the proposed rules (heavily copied from Keep on Truckin's rules):
The Rules and Regs
1. Civilian TRUCKS only. No military trucks unless they are clearly in "every day" civilian use.
2. Must have two or more axles.
3. Trucks may be OOB, highly modified, or tricked out.
4. All makes & models of trucks are allowed.
5. Trailers & loads are optional.
6. Scales from 1/72 up to 1/6 allowed.
7. Build pictures have to be posted showing progress - minimum of four pictures of the build and two for the gallery.
So, basically from an 18-wheeler tractor down to a little pickup and everything in between. If you have something larger than an 18-wheeler tractor, by all means, build it for the campaign.