I had a 2000 Cougar which is made by Keystone and had the same problem. Dealer said it was normal to smell when first opening the door even though it is venelated from the bottom. I thought gas fumes went down. they checked and found no leaks. I also checked all lines, fittings with liquid soap and never found a leak. Dealer said it came from pop off or whatever the valve is called but, never could get a bubble there either. Kept the Cougar 2 yr and it never blew up Have it checked good or better yet check it yourself or have a propane gas company check it. Take no chances.
I have a 89 Winnebago that I have been smelling fumes for about a year. Finally found where it was coming from. The LP Leak Detector actuator for the shut off was leaking a little bit. I tried to fix it by cleaning the threads and replacing the "o" ring but it stilled leaked. I had to replace the entire unit and it fixed the main smell problem. When my hot water tank runs....right after it shuts down, I do get a little smell, but I think that is just burned LP smell and not a leak. I have checked all connetions with soapy water solution and no leaks. Everything seems to be running just fine (stove, hot water, furnace, etc.). Make sure your leak detector inside the unit is working properly (I use propane lighter and hold it right by the detector and if it is woking, it will trigger alarm and shut the gas down at the turn off (the one I replaced)). Test it and if it not working, replace it. You can never be too cautious with LP. Too much riding on it.
TEST AND RE-TEST. Good luck