Obsolete RV Furnace

I have a SOL/Aire furnace as far as I can tell. The unit runs and heats fairly well. The problem is when it starts up the first time and for a while after. It starts good but backfires on startup. The blower comes on and then it will start to pop. Gas pressure is correct and all other equipment runs good. Someone suggested I check for cracks in fire box?
Dick, (Schenectady, NY)

Dick, as far as I can remember, replacement parts for Sol-Aire furnaces are no longer being produced, including the firebox/combustion chamber. Unfortunately, the Sol-Aire had a propensity for the burner to literally burn away during those popping instances. According to some, it had something to do with the design of the burner. And over time, those mini-explosions would eventually blow a hole right in the burner mesh. You may be able to find some repair centers still with replacement parts, but it would simply be hit and miss I’m afraid. The best bet is to begin searching for a replacement furnace that will fit in that same location. I wish I had better news, but obsolescence is something that just happens within the world of RVs from time to time.