@rickhise - I unfortunately do not understand HVAC hardly at all and am using the stand-alone heat pump right out of the box with only the exhaust venting going outside the rig. I know that the unit is pulling air in from the outside for this venting, but I do not know how to supply outside air to the unit.
@RedRocket204 - thanks for the info! When I changed the bulbs in one of my ceiling lights I discovered cool air coming out of the gaps in the housing. Clearly the ducting is leaking in likely more than one place. I'll definitely look for the leaks and fix them up.
