RV Repair: Rmoval of SF-27 Furnace in 1999 Bounder, b vent, vent pipe

Question
We need to replace our furnace in our 1999 Bounder. We have removed a ton of screws from the furnace attaching it to the wall. It has been extremely difficult to get to some of them. We finally got out the last hidden screw at least we thought... but it still won't come out. I'm sure there must be a secret to this... if anyone could help we would appreciate it! We can't afford a service call.
Thanks

Answer
You may be held up by the vent.   That is a B-vent and has a second pipe inside the first.  These pipes can get caught up on eachother.  Look from outside and make sure there is not something else causing trouble.  You may have to remove the inner vent pipe before the outer one will release.