Smoldering fire behind refrigerator

Hello there. Long time no post, but here I am again. Recently purchased a 1990 Vision Class A, and it was a nice deal on a nice coach. I have been going through it trying to find any minor issues I can remedy, since it had been parked for two years.
I ran the refrigerator (a Norcold 2-way) on AC power for a day and it worked great. Then I decided to check propane operation. It lit right up and I ran it for a few minutes but it was late in the evening, so I decided not to leave it running overnight.
The next day I started it again and within about 15 minutes my girlfriend alerted me that there was a fire somewhere. I discovered that there was a smoldering fire in behind the burner chamber.
Luckily I had an dry-chem extinguisher handy and I had it put out quickly. We have a yellowjacket (wasp) problem in my area and there were several of them seen leaving the refrigerator vent on top of the coach. Those darn things will make nests anywhere they can get to, so I'm thinking they could be the culprits.
Regardless, I am a little scared to start it up again. I took the shop vac out and cleaned it out the best I could. A small amount of debris was removed but no smoking gun was found.
I am hoping somebody here has had this experience, and/or can advise me what I should do next...