You've got some good work going on with this one, Man....As stated earlier, judging by the skills you've displayed with the weathering, alone, I'd say you've got what it takes to scratch up one of those trailers.....And as far as the CAT Challenger, you might want to check Bruder Toys for a 1/16 scale tractor as a starting point....They have several in 1/16 scale that might work....And they're pretty realistic....
I scored this one for about $30....