I don't think I would mess with the outside outlet of the Furnace... I would put more effort is doing a positive air flow thru the cabinets and other areas by installing pass-thru air vents and the use of a temperature controlled vent fan.
In my OFF-ROAD CAMPER all of the cabinets are lined up around the walls of the trailer. I have added a small vent between all of the inside cabinets walls. Having a large vent close to my access door door I can circulate air through the whole thing... Adding a thermostatic controlled blower works wonders here... This way I don't have to open cabinet doors to allow heating of water pipes etc...
Got this idea from one of the full time RV'ers Don or Mena...
Roy Ken
