Humm,,, I'm no expert but, I think you could have found a fridge cheaper then that.
Anyway, For safety reasons I have to tell you to replace the furnace. AND!!! I really, really, do recommend that you buy a carbon monoxide detector and put it in your camper. I have one in my camper and beleive everyone should have one. And, you better have one for sure!
That being said, I wonder why the last person was cutting away at the tin. You may not be the first one to have had this problem. If it were me I would do the same thing and see if you can do a better job then the last person did. But, that's just me.