Not too uncommon........ Where is the furnace located relative to the furnace?
Mine is the living area and has a long run to the bedroom.
Try a couple of things.
Block off ALL vents except the bedroom, does the flow/heat improve?
If not, the ducting may have come off - check the ducting all the way between
the bedroom and the furnace.
If the flow improves then the ducting is probably okay; You then have to partially block some of the other vents so as to balance all the flow to each of the rooms. I did this putting duct tape to partially cover the vents closest to the furnace.
Been like that for years now and the whole camper stays toasty
gerry