Jeremy,
Here is example of pup that may work with your Van. Too bad it can not use a wdh hitch.
227 - MAC/LTD Series 12 foot box
Dry Hitch Weight 293 lbs. (133 kg)
Axle Weight 1,713 lbs. (777 kg)
Unloaded Vehicle Weight 2,006 lbs. (910 kg)
GVWR 2,972 lbs. (1,348 kg)
Cargo Carrying Capacity 966 lbs. (438 kg)
Box Size 12' (3.7 m)
Exterior Open Length 23' 10" (7.3 m)
Exterior Closed Length 17' 2" (5.2 m)
Exterior Closed Height 4' 9" (1.4 m)
Exterior Width 85" (2.2 m)
208 - MAC/LTD Series 10ft box
Dry Hitch Weight 219 lbs. (99 kg)
Axle Weight 1,518 lbs. (689 kg)
Unloaded Vehicle Weight 1,737 lbs. (788 kg)
GVWR 2,603 lbs. (1,181 kg)
Cargo Carrying Capacity 866 lbs. (393 kg)
Box Size 10' (3.0 m)
Exterior Open Length 20' 1" (6.1 m)
Exterior Closed Length 15' 3" (4.6 m)
Exterior Closed Height 4' 9" (1.4 m)
Exterior Width 85" (2.2 m)
They are not listing water storage. My glamping classic 625d had 26 gallons of fresh, 6 gallon black cassette and no gray.