I thought about doing this since we camp in cold temperatures on our way South for the winter. We get our start after the holidays.
If I insulated the heater ducts in the "basement" of the 5th wheel there would be much less heat in there and our stuff could freeze at night. The water pump and filter is also in the "unheated" space directly behind the sink in our floorplan.
We even leave the undersink door open to allow more heat, bedides leakage, to get into the basement to keep the lines from freezing.
Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW