Are you sure your front house heaters (not the chassis heaters) are all on?
Given that you have a DP, I wouldn't be surprised if you had a 2 zone (or more) system. Make sure you are getting air out of all your vents - and that its warm. Make sure that you don't have to turn on the front zone in addition to the rear one.
My coach has 3 zones - bedroom, bathroom, and living area. All 3 have to be on to get heat to all of them. Granted, I can usually turn on the front and rear and be fine. But, in freezing conditions, I may have to run all 3.
What kind of heat do you have to heat the coach? Is it a propane furnace (sounds like this is the case)? Aquahot? Something else? Make sure you have just 1 before taking other measures - there may be a second to heat the front of the coach.