Whats the right way to adapt this air intake and exhaust? (propane furnace for RV)

I have no HVAC experience and I need to make extensions for intake/exhaust pipes. These are pics of my RV furnace

the exhaust and intake plate goes on the outside of the RV, feeding those pipes into the RV to mate to the furnace (sliding over the corresponding pipes on the furnace side). On the furnace side, the upper (male) pipe is metal, and the lower (male) pipe is plastic... I assume this is the intake. The instructions dont say anything about sealant, but do say to overlap 1.5 min. I'm surprised by this since they just slide over each other, and while its somewhat snug, its not exactly a super tight fit considering the upper pipe is for exhaust fumes. Should there be additional sealant?

The unit and exhaust/intake ports is total about 23-24" long, my cabinet that id like to install this in is about 30" deep. The front of the furnace needs to be at the front face of the cabinet (thats where the air blows out of).

So I have a 6"-7" gap I need to cover with some sort of exhaust and intake extensions, the upper one needs to be able to handle the heat of exhaust.

• 1-3/4" - 1-7/8" pipe diameters
• 16,000 BTU furnace (exhaust)
• Suburban NT-16SEQ furnace model

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Thanks so much for any help on this, as a secondary question I also havent figured out the right way to connect a gas grill style propane tank to that connection, is this a standard fitting?

submitted by /u/eggs-benedict
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