my GMC 6500 weighed 12460 Cab and Chassis ft 5860 rear 3100
stretched as a flatbed looking truck before I added the box and interior, ft 6320 rear 6140
finished full of fuel, 75 gallons, ft 7420 rear 12220
ran it across a closed DOT scale house the other day, ft 7760, rear 12220
22' box 35 gallons fresh water, 75 gallons fuel located behind rear axle.
Your milage may vary
wow I just notice my rear hasn't changed with al the work I've done to it. Cool!