My 10 gal. Atwood was fixed at 140 and it was touchy to set at an unpainful temp so I used the control in the previous picture and wired it in serious with the oem temp control and set it at 120. Now the oem 140 control is the hi limit. Our shower head shutoff valve works fine and both of us can easily take the showers we like, one right after the other.
Then the 14 yo element bit it, so I used a folded-over style 240vac 4500w element. Now it is SUPER low watt density and pulls <10 amps and it still heats plenty fast. Craig