The AMT van trailers and flatbed are your best bet, next finding a glue bomb or discount on ebay.
Heres my Ca Hauler with the AMT flatbed. I added scratch built quarter fenders and the reflective DOT tape, otherwise its box stock.
Another Ca Hauler i built. I used the AMT beaded side van trailer. Its all box stock. It comes with a nice decal sheet.
Here is my snap pete. I switched the wheels and tires for moebius, lowered, shortened, scratch visor, stacks, and bumper, resin fenders. These kits are good to start with. I think of then as a blank canvas for creative freedom. Theyre affordable, easy to put together and allow a builder to try new things on big truck kit. Im gonna be starting a KW soon, maybe after i finish what i have going now.