The furnace is most likley a Suburban NT30.
It is really not that hard to replace. If you are a bit handy with tools and can be careful when hooking up the propane you are set.
The New NT 30 will swap right in.
1. Buy new furnace
2. Get to the old furnace. This can be the hardest part.
3. Pull the cover (inside), normally 2 screws.
4. With the LP off, dicsonnect the LP, and the 21 volt wiring from the isde. Disconnect or detach the ductwork from the air box
5. Remove the 2 screws that hold it to the floor, these are also in the air box. ( you may want to wait to do this until the exterior vent is pulled. Having the furnace held in place can help on its removal.
6. Remove the exterior vent center screw, You will get a new exterior cover so you should replace this too. 4/6 more screws to pull.
7. Remove the exteror vent cover and its two tubes. This is the hardest part as they are normally rusted together.
8. Then you can remove the furnace.
Reinstall is in the revverse order but you will need furnace tape to seal the furnace exterior vent. And I would be sure to have the vent installed and the furnace in place before screwing it back into the floor. Also be sure to get it all the way into the wall cutout. Airstream cut these close in some cases so it may be a tight fit.
BTW on the new furnaces the old thermostats work fine, the old plug will plug right in. The new ones look cheap and are made from white plastic. The only thing is there is a switch that you need to turn on, on the furnace chassis that access is thru a slot in the side. It is red, so it is not hard to find on install but depending on the final position it may not be accessable.
Even with my wonderful
directions if you are not comfortable in R&R the gas lines or the furnace in general have someone who is do it. The $$ saved do not make it worth the loss of sleep worring over it. Propane CAN be dangerous.