[Ozarkguy]

Get a Digitial Inspection Camera from Harbor Freight (about $80 on sale) take a look for problems. Then turn one on n see what happens. Chances are they weren't used that much as most find the electric heaters keep the coach warm enough. Then follow Toms suggestion. Mod/replacement would be my last option if I didn't want to cut.
I ended up replacing all my electric heaters (there are post about them) and kept my original furnace.