for the semi truck trailer you can open up the back and be able to place what ever and store what ever but for the truck being able to hitch to the trailer is a bit fuzzy in my mind but please consider it at least. and there can be different bed types like there could be a fuel canister bed for storing fuel or a flat bed trailer, go crazy with it hell if you want make a machine gun or cannon trailer but if you were to make that it would have to be found in the military bases. Post comments of different types of semi trailer variants if you were so to desire