The rear seats alone weigh in at a beefy 200+ lbs (I had to ship a set). All the interior trim and carpet (assuming it was removed) is easily another 40-50 lbs. A Disco's body isn't too heavy, the removed section was probably another 50-60 lbs.
A stock D2's payload capacity is 1,500 lbs. The frame is very sturdy, especially in the back half. The weak point is the suspension followed by the axle, and both are easily upgraded to handle additional weight. With the proper upgrades the capacity can be boosted to around 1,900 lbs. Between upgrades and the material removed capacity could be safely pushed up as high as 2,300 lbs.
Spending 1,200 lbs on the camper from that point sounds pretty reasonable, especially when you start factoring in all the gear that doesn't need to be carried with all the built-in systems. Just add food, water, clothing, and people... and hit the road.
I'd be curious to see how CoG is affected, and how the truck handles a crosswind with the extra height.
