I think what we have here is a misunderstanding.
If an A/C unit like a window unit has no outside air to dump the heat
into what you have is a dehumidifier.
The kind of unit under discussion is the "roll-around" type that is used
like a space heater, only for cooling not heating. It has to have an
outside vent to blow the hot air coming off the condenser out of.
A/Cs have two entirely separate air circuits. The evaporator is the
"radiator" looking thing (actually absorber) on the inside. It gets cold
and the air for the interior is blown through it, chilling it. The
condenser is the radiator on the outside. It gets hot from the heat being
pumped via the refrigerant from the evaporator to it. Outside air is
blown through it to condense the gaseous refrigerant, whether it be freon
(now illegal), R134a, ammonia (used in old units and large commercial
units). The air coming out of the condenser is hotter than the air pumped
into it.
I have seen some of the "roll-around" "personal" A/Cs and they drew the
condenser cooling air from the interior of the house. This air has to
come from outside or the windows or walls of the house would be collapsed
(not really - if in an airtight house the unit would simply be unable to
blow any air through the condenser). In house applications it appears
that the hot outside air infiltration is tolerated for the sake of a
cheap, simple single exhaust hose. The purpose of these personal A/Cs is
to blow cool air on the person they are pointed at. That the rest of the
house may be warmer as a result is not of concern. That cooled air that
has just been chilled with electricity, which is not free, is used to
carry the heat out from the condenser is ignored.
But using one as an RV A/C that is presumably intended to cool the entire
interior will result in one cool spot where the cooled air is blown and
the temperature of the rest of the trailer being raised by all that
outside air coming in.
As to needing air exchange, we don't need al that much. Most trailers are
pretty drafty anyway. I've been plugging cracks and wiring passages with
non-hardening plumber's putty and it made a difference. A trailer would
have to be built to house "Energy Star" - like standards, practically
hermetically sealed, before air exchange would be a concern.
Automotive primary A/C is not comparable to building and RV A/C. Unless
"MAX" or "RECIRC" is selected all air for the evaporator is drawn from
the outside at the base of the windshield.
In my van, the front A/C is conventional automotive while the rear A/C -
heater unit is recirculate only.
My Dad had a '55 Caddy that had 2 A/C units. The front inhaled from the
cowl (base of the windshield) and the rear unit, mounted in the trunk,
drew its air from little scoops on the rear panel between the rear window
and the trunk lid.