One thing that'll help the renders look better dude... if you open up I think it's the 'XR_INTERIOR1.DDS' (or TGA if you converted it) file in Photoshop or whatever, you'll find a small white square outlined by a dark colour. Paint that white square either black or very dark grey. It's the area in the texture used for the likes of the window rubbers, the rear diffuser, under the wheel arches etc.
It's the same for all the cars, so you'll need to do it for each one, but will definitely make the render look better and more realistic
I'm no modeler but I'm sure you'd be able to use some custom models from the 18 Wheels of Steel series. Bit more selection if you'd prefer a euro truck instead of an american beauty (yes I know big american bull nose trucks do look awesome).
I know most people use Zmodeler to make them but I'm sure theres some people out there who use 3dsmax or the like.
No doors, you gotta get in Dukes of Hazard style. I tested a skin on it and skins work on it, but anything going across the doors is gonna be missing and anything that goes from the front wings onto the door, or from the rear quarter panels(sp) onto the door is gonna look pretty messed up. I also chopped the windscreen and added a stalk to the rear view mirror and flattened the rear seats.
I've been up all night talking to my mate in Oz and copying your Rod C4OZ. I think the roof is lower on mine and I added the LX seats and customized the LX exhaust. I wasted a couple of hours talking and changing wheels on this thing, I got rid of the wing mirrors and im gonna make some up for it. I had to make a tyre for the wheel too.