Old Bisquit says
You have a Suburban water heater.
The OEM factory ON/OFF switch for electric heating is in lower left corner in outside compartment. Unless RV MFG installs an additional on/off switch inside that is the only one.
You can install one inside (vs moving that one) in series with that OEM one.
Stop using the 120V AC circuit breaker as an On/OFF switch.
There are ones designed for that 'abuse' but the ones used in RVs are NOT and you will be having to replace it
most all MH I have seen/owned/repaired had a propane electric combo switch on wall inside MH. Using the breaker a few times a year for turning off hot water element will suffice very nicely if no auxillary 120V switch was installed .I mean really how often does one turn off the HW when living in the RV