Due to the large amount of power used by the inverters in our coaches, the 12 volt supply to them is not switched. Turning off the house batteries, DOES NOT shut off the power to the inverter. The newer coaches have a 300 amp fuse in the 12 volt hot line to the inverter and the older coaches just had the fuse in the ground line.
As to where to get Aqua Hot parts, have you checked with the manufacturer? Here is link to them.
As to other questions, others are covering that for you.
I will try to be clearer in my posts, I am a lazy typist and try to get it all out in few words.
I lied, in my post about being retired, I am only semi-retired. We are in Oxnard, CA enjoying living in the coach, but working hard on a rental. Don't have a nice lake view here, but Yum Yum, our cat is with us as always.
I hope you get to start enjoying your coach soon.