I've seen this documented by several other folks on this site, and I had my own experience yesterday.
Last outing the 110v side of the water heater didn't work. Put it on my to look at list.
Last night I dug in. On my RV the WH is under the sink. I pulled a panel that keeps pots/pans from sliding back to the WH and such, then I had to drain the heater as the access to the plastic box on the back of the WH was blocked by the cold water line. After pulling the plug and then the lines, I opened the box to find a mess. At this point I turned off the circuit breaker to all AC in the coach as I don't trust thors breaker panel labeling yet.
Inside was the 3 wires for providing power to the element in a semi burned/semi melted mess.
Here is a closeup of the wires after I pulled them out of the mess.
So I cut the wires off on both sides to get to good unmelted wire and instead of using normal wire nuts I used Ideal Mechanical Connectors ( 30-1294G )
These brass connectors have a set screw that is what holds the wires together. Had I really been thinking I might have lock tighted them as well, but whatever. Here is an example of one before the cap is put on (and before the excess wire is trimmed).
After I screwed the plastic cap down (using pliers to hold the wires so they didn't twist) I added tape to keep anything from getting into the wire nut from below.
(sorry no picture, but I assume you know what a wire nut with electrical tape on it looks like).
I put everything back together and now my water heater works and I don't have to worry about a fire.
BTW, a parting look at a melted glob of wire nuts to scare you.