Access to the furnace is from the outside via the removable screen covering the device. While there is no pilot light, there is an igniter for the burner. I am not familiar with your floor plan but I would be surprised if the furnace is under your couch.
In the Files Section (second thin brown ribbon above)
https://www.montanaowners.com/forums...hp?do=cat&id=1 are a couple of files that may help you diagnose the problem.
atwood propane furnace.pdf
Atwood Furnace Training Manual