You can actually tear into the furnace quite a bit with the proper knowledge.
I just found the
Atwood Mobile Service Training Manuals PDF when looking for something else. It covers ALL of the Atwood products and is quite technical but written such that regular folks can read it and understand.
The troubleshooting section for the furnaces is quite extensive. Between that and the exploded diagrams and parts lists, I think you have a clear path to disassemble and reassemble just about everything they sell.
Chances are, you have an Atwood 7900 Everest series furnace but you'll need to confirm.