Nat'l Tradewinds 2002 LE - Furnace Replacement ?

[dansawyer]

The RV is a 2002 National Tradewinds LE 2002. The furnace is a Atwood 8535 IV DCLP, install from the outside. I ordered a replacement which turned out to be an install from the inside.

The basic core of the two furnaces appear to be common.

It does not appear as though it is straight forward to move the outside flange from the original to the replacement.

I have thought about cutting a flange from sheet steel and using the 4 mounting brackets to attach it.

Does anyone have experience with replacing an externally installed furnace with one designed to be installed from the insied? If so what was your experience and what worked?

Thanks in advance, Dan

[dansawyer]

Update:
I missed the construction / attachment of the front 'external' fitting / adaptor. It is held on by 6 tab fingers. There is a significant amount of gum like caulking compound. So some progress.

The remaining issue is: the new furnace comes with two plastic covers covering the exhaust 'chimney'. However with the adapter installed the plastic covers do not fit. Has anyone solved this particular step?