I think another variable people aren't considering is tire size and it's affect on braking. I guy towing 5000lbs on 40s is the same as a guy towing the same weight on stock tires.
The brakes are by far the weak link imo. Ive towed close to 8000 pounds cross state with my swap and 7300 lbs from Florida to Cincinnati, but I wouldn't do it without good trailer brakes. The only thing that might get you is the wind resistance of that camper with the stock motor imo. If you ls...
One of a kind 6.0L vortec max built trans swapped Land Cruiser! Swap was done right at 300k with the donor engine at 130k. Trans has less than 1000 miles since rebuilt. 3 linked front suspension on trussed axle with lockers front and rear. Custom front bumper, nwti rear and white knuckle sliders...
Not much, don't have pictures but it was the lip of the front and rear of the rear wheel well to make it flush with the lining for about 6 inches from the bottom edge. The front I stretched forward and cut the front clip out in about 12" and up about 4".