This may have been the case a long time ago.
A long time ago RVs didn't have grey water tanks either - they dumped
onto the ground if there was no park sewer to drain into.
Today we consider that a faulty (or just antique) setup.
Used to be that the 115VAC neutral (white) wire was grounded to the RV
body/chassis/frame. The ground wire (if there was one) was likewise
connected to the RV chassis/body/frame. Today this is not allowed. The
115VAC must be totally isolated from the frame/chassis/body of the RV and
grounded only to the land power neutral and ground. The old way,
grounding to the RV frame/chassis/body could get you electrocuted if the
land power polarity was reversed (defective wiring setup). It also could
allow 115VAC to get into the 12VDC wiring system.
If there is an access door to the burner part of the LP refrigerator it
can have louvers formed into it or can be replaced with a louvered door.
If you don't want to alter the original appearance a vent can be cut in
the floor opening into the underbody space, which is unlikely to be
airtight.
If there is any space around the refrig. installation going into the
interior it should be closed off as airtightly as possible. The back of
the refrig. should be open to the outside.
Of course a LP refrig. will work with interior air. We used to have an
enormous Servel absorption refrigerator in our home kitchen. It had an
electric heater in place of a gas burner. It certainly wasn't vented to
the outside. If it had been a gas model not only the warm air off the
condenser but also the exhaust from the burner would have gone into the
kitchen. This was not unsafe in a house installation as no one slept in
the kitchen, and there was a lot more air for it to be diluted by. Our
entire trailer is smaller than the kitchen in the house.
Al