Weight isn't really the problem because there are insulated delivery TC's running around with reefers on top, but you're basically going to freeze yourself out, lol. That unit is 13,500 BTU; consider the fact that a 5K BTU window unit in a house can easily cool 150 square feet (times 8ft tall for typical ceilings, so 1200 cubic feet and our vans only have 166 cubic feet of cargo volume, plus a little bit more for the front seat area, lets round it to 200 cuft total).
IMO, you'd be better off with one of those new portable AC's, instead. This "Zero Breeze" Mark 2 unit has good reviews online but is spendy $$$ and seems to be pretty decent for what you'd be doing and it's battery-powered/portable, weighing just 16.5lbs (Coleman Mach 3 roof unit is 90lbs, for comparison). Our vans have a total cargo capacity of roughly 1250 lbs or less, depending on specific model and features, so weight is an important consideration when building a micro-camper and still being able to carry everything you'd like to - including yourself & any passengers - without exceeding GVWR.