Editing models is a good way of getting the hang of a program or modelling in general. I used to do that with NFS IV cop cars, I was deleting the cop equipments to get a civilian car.
Also, a little progress:


Decided to add some hubcaps anyway. I don't think I'll add whitewalls, after all these are working trucks, not some toys. Also, I was thinking about randomised loads for the trucks. So each time you spawn a truck, you'd end up with some random junk in the back. Good way to add variety, I think.