fridge and furnace

[shinobi]

We're new to the whole pup ownership but we have a '79 Viking Saga but were wondering if it's possible to install a propane furnace or fridge into the trailer? It came with an icebox but we took it out how does the whole thing work? are fridges too big for the viking? or is it impossible to install a furnace into it? I'm asking because I can get them used for cheap. Thanks
Ad-on: I missed the deal but I'm going to keep an eye out for the next time