Should be receiving a Mar-K bed next week for a '53 3100 and have heard two options on the assembly. My question for the experts: Is it better to assemble the bed on the truck to assure correct fit/dimensions or to assemble the bed "on the floor" then mount the assembled bed on the frame? I had thought assembling the bed on the frame would be best, but since this is my first experience with bed construction, your recommendations would be appreciated.