When I went thru this 4 years ago they were looking to make sure its not built from stolen materials, not looking at safety or anything like that. Keep the VIN plate from the door or the cab as well as the bill of sale for the truck and the receipt for the axle and you shouldn't have any problems getting it inspected.
Honestly though I've found pickup box trailers not to be that great of a trailer for the work that goes into them. They end up being WAY heavier than they need to be for the weight they can carry. Think about it, you're dragging around half a truck. ok minus the engine and drivetrain, so a third of a truck? By the time you buy an axle and hitch you're around the same cost as a used trailer.
Now if you're doing for the cool factor of matching your Jeep thats another story......