Sorry for your problems...I often wonder why furnaces never seem to act up and break down in the summer time!
:S:W:R
I asked a wise old sage (yep..older and wiser than even me!) to read your past and add his two bits worth...he has owned a RV Repair Service here in SoCal for many, many years...
He said that only a qualified repair guy like himself can check for possible issues that could be caused by low LP gas pressure which can be from a number of factors, including a malfunctioning regulator, clogged or restricted propane lines or low gas levels in the tank. This can ONLY be tested by a qualified service technician.
And low voltage can be an issue, which again can only be checked by a certified service technician.
Please note that RV Salvage yards carry furnaces removed from RV's that have been "totalled" from wrecked or damaged RV's that are in perfect, undamaged and fully functional shape..for about half of a brand new unit.
Ericksons RV Salvage in Coeur d'Alene, Idaho (208) 664-8902 for example. The great part is that RV Salvage yards can do a local or national search for what you need from other Salvage Yards. Good luck and bundle up!