humm, I always thought four-way meant: 1) electric, 2) battery, 3) ice, 4) propane
I made up the term, so that may be the case. Perhaps multi-way fridge, then.
As to having enough space for it, it seems possible to mount the compressor away from the fridge itself, so I wouldn't see that aspect of it as an obstacle unless everything else is already cramped. And the cooling plates seem bendable to a certain extent. Would have to try it to find out, I guess.
But, but but... I also saw some prices for those conversion units