If you would rather not have to go outside to turn it on and off, and also not have to wear out your circuit breaker by using it as a switch, you could also do this mod as an alternative. It makes life with the HWH much easier.
"How-To" reprint from a previous post, when I did this mod several years ago:
(Using a circuit breaker as an ON/OFF switch is not good for the breaker. Using it for that purpose repeatedly will eventually wear out the tripping contact and sooner or later the breaker won't hold in the ON position. The breakers that Casita
installs are designed as intermittent use devices. They are not, and do not, replace regular toggle switches which are designed to be cycled on and off regularly. That being said, an alternative to having to go outside and turn the HWH on and off with the switch on the top of the unit, you may want to consider installing a regular switch with a "Power On" indicator light
inside your trailer, which is actually made to be cycled ON and OFF regularly. I find it very convenient to be able to turn it On and Off from inside, especially when the weather outside isn't very nice. This was a mod I installed years ago, and it has been posted several times when the HWH switch question arises.)
Remote HWH 120 VAC Switch installation (for turning the electrical element in the HWH on/off from inside the trailer.)
You will need a 3 terminal single pole pilot light
switch, (it has 2 brass screw terminals, 1 silver screw terminal, and a green ground screw terminal.) Leviton makes one, (link below,) with a switch on top and a red pilot light on the bottom that fits a single electrical
switch box (see pic below). You can find them at any "big box" store. You will also need a length of 12/3 w/Ground Romex wire, and an "Old Work" style plastic electrical box in which to mount the switch. (These are the style of boxes that slide into the cutout and have twist-out ears that secure the box to the wall when the screws are tightened.) The length of Romex you'll need must be long enough to run from the converter panel to the location wherever you decide to mount your inside switch, plus enough extra to route it along the existing wiring bundles and to make up the terminal connections. FWIW, I mounted my new inside switch on the footwell side of the rear side dinette bench, out of the way of getting bumped.
First: Remove your shore power connection to make sure that there is no 120 VAC power going to the trailer. You don't want to be working on energized equipment.
Remove the existing black wire from the HWH circuit breaker's screw terminal and just move it to the side for now. We'll come back to it later. Using the (new) Romex wire, take the black wire of the three insulated wires, and wire it from from the HWH breaker terminal screw in the converter panel to one of the two brass screws on the new switch. The red wire goes from the other brass screw on the new switch and is wired back to where it reconnects with the original black wire that was removed from the breaker terminal that you removed earlier, (see, I said we'd come back to it.) So, now you will have a black and a red wire. Twist these two together, wire nut them securely, and tape this connection well. OK, now that takes care of power to the HWH from the new switch. So now we need to hook up the pilot light on the switch. The switch itself needs to have a neutral wire in order for the pilot light on the switch to come on when the HWH element is energized. We will use the white wire for that purpose. One end will attach to the silver screw on the new switch. The other end of the white wire goes to an empty screw on the neutral bus in the main panel below the breakers. Be sure it is on the neutral bus, not the ground bus (Yes, they are not one and the same.) Lastly, the bare ground wire is attached between the green ground terminal screw on the new switch and an empty screw terminal on the ground bus in the panel. Since the ground wire is now potentially a current carrying conductor, be sure to tape up or heat shrink any of it protruding from the wire sheath to prevent it from being a shock hazard, leaving just the ends that attach to the terminal screws bare. Don't forget to leave the little switch located on the top of the HWH itself in the ON position at all times to make it work from inside, because power still goes through this switch on the HWH itself. It's just a lot nicer to not have to go outside to turn it on or off each time you want hot water. The switch with the pilot light isn't absolutely necessary, but it does give you that all-important indication as to whether the heating element is energized or not. It's a good reminder to remember to turn it off prior to draining the HWH and frying your heating element.
The switch I used:
(And the cover plate needed for this switch is one made for a standard duplex outlet, not the normal stand-alone switch cover plate.)
The "old work" electrical box I used: