Actually, having seen the kitchen cabinet on a U-haul
(which I think is the same as a Burro), I don't think there would be much difference in sealing off the fridge on that than on a Boler/clone that is not "double hulled." That's because the kitchen unit on the U-haul/Burro is still "open" in that it is open to the rest of the kitchen unit (and, in fact, probably even more open to the rest of the camper behind the rest of the "double hull." The lower kitchen unit on my Boler
is essentially sealed to the outside walls all around itself, but I could still easily get combustion byproducts into the camper through the stove openings, the lower cupboard doors, the drawer, etc.
On my boler
there is an aluminum (or maybe it's galvanized metal - in any case it's like HVAC ductwork metal) enclosure that runs around the sides of the fridge and seals it off from the rest of the kitchen cabinet. I don't think it's hermetically sealed, but it is probably more than adequate. You could probably accomplish the same thing with plywood and duct tape, although it wouldn't be elegant. You could use metal ductwork like in the Boler
, or fiberglass tabbed to the hull, or etc.
A cooler is darned simple though, if you have access to ice blocks, or can make them. And you can move it outside if you cook out there, and take it back into your house to load up, empty, or clean; so they do have advantages.