Yes I did have a fire with our first motor home
HERE. It was under the hood of our little Toyota chassis. The solenoid that switched between batteries failed, burned up and smoked, leaving behind black soot on the inside fender wall it was mounted to and on the hood above it, fortunately with no paint damage. It did melt the wire harness jacket below it but did not damage the wires inside. I got very lucky with that catastrophic failure.
On our PC, we have a similar looking device mounted near our fuse panel in the house, I think under the fridge. It is the thing that makes the loud "Click" when turning the main house power on/off, along with that loud chirp from the propane detector.
I suppose there is a threat of a similar failure, but I never gave it a serious thought.
The solenoid thingy looks something like this.

On the Toyota RV, I replaced it with a battery isolator that looked like this.

Circled in red, you can see where the original solenoid was with the two mounting screw holes caulked, and the wire harness below it, and also the replacement blue isolator. If you look close, you can see the black wire harness jacket is deformed/melted.

I have no plan to change the solenoid on our PC.....not yet anyway. I am not even sure if the one in our PC is used in the same manner as our old Toyota chassis rig.