Would you mind turning off your "Caps Lock", it makes it hard to read in all capital letters and some consider it shouting on the forums.
If you are talking about the breaker on the front of the inverter, it protects the inverter and the inverter charges your house batteries. On my Xantrex Inverter/Charger it is a 25 amp. breaker.
Now about your water heater door loss. It has happen to many, including myself on our first MH. There are some when you stop at a rest area or other places that will turn the spring loaded latch because they know the door will fly off when you are traveling down the road. Really funny they think!!!
What I have done to prevent this is that I drill a hole right above the latch in the slot and install a stainless steel screw. This prevents the latch from being turned easily and also keeps the door from coming off. The only drawback is that you have to remove the screw to remove the door to service the hot water tank. But this is a minor inconvenience compared to losing the door/cover.
We are all here to help as the forum motto says: "Gulf Stream RV owners coming together to help each other!"
I figure that we all are the experts here on the forum since we use our RV's and learn our systems sometimes the hard way.