I took the panel (wall) in my 38FL basement off that has the central vac motor on it and have a clear shot into the under part of my coach and all the duct work. There is also power right there behind the wall for the vac to plug into. I tapped that power and put an extra plug down by the floor in the kitchen, but that's another story.
Anyway, could be just cut a hole in the panel, install a bathroom ceiling or other wall fan to circulate the air. Add a radiant heater in the basement like Dave does and the air moving around might really be warm.
Could be a fun project I'd just make sure to have some good screens on the fan so small things don't crawl in during the warmer months.
Redwood 2015 38FL,
Ford 2015 F350