I was out puttering around the camper the other day and saw a wasp hanging around the vent on the water heater. I thought to myself "that guy is looking for a place to build a nest". A couple days later I found him and a small nest started in the corner of the opening.
My solution was a piece of cheap aluminum screen. I bought a roll of screen from Home Depot for about $6, it was the smallest repair screen they offered.
I used RED high temperature RTV because this door will get very hot and any other silicon will break down and fail.
I timed a one hour wait before I pulled the tape off. In retrospect I might only wait 30 minutes next time. The RTV had dried too much and wanted to come off on the tape. Razor cutting the edges did help get the tape off. The wasps will not be making next in our water heater any longer and no holes in the door to look at.