My rig came with a 6500 watt Onan mounted in the side in a truck box. I sold the Onan and repurposed the box. Boxes can be made in any size you want but you would have to have the stones to cut thru the side of your van. I like my setup so well that I'd cut my next van in a heart beat. Quick search on heavy truck boxes and I bet you can find a black one.
http://www.pickupspecialties.com/toolboxes/Unique/brute_hd_underbody_swing_door.html
Mine is mounted obove the floor but the inside space under it is used for electrical and house batteries.
I insulated the inside with those rubber floor puzzle pieces from Home Depot the cut thru the inside to mount the AC.
I used expanded steel to give the AC fins some protection.
Inside a framed enclosure surrounds the box. The front panel drops to expose underneath battery storage.
The counter space is multipurpose and well used with a shelf obove it.
A 25 gallon water tank sits under the bed behind the wheel well to feed a bar sink I mounted on the side of the encousure. The blue Scepter water jug is grey water and is a good color for stealth dumping.
It's all came together perfect for my home built interior but I bet you could find or have made just the right size truck box made for your needs. Somebody could put one behind each wheel well at floor level and it would be the right height for a bed. Sky's the limit and yes you can cut it and mount it right with the right tools or pay a local body shop to make the cut.
