I'm afraid I'm of no help with the hot water issue....Was there no hot water heater in your coach at all when it came out of the factory?? Like there's no dead water heater in there now?
If so, just from my limited experience, adding HW is probably going to be a challenge....not impossible but a PIA for sure. The way these things are built make them really hard to get at installed systems/wiring......in mine the main wiring run (bundle) was put in and secured to the floor...THEN they installed the hot water heater OVER it....good luck with changing/tracing anything...gotta live with it as is....
You having a charge controller is probably a good sign....sorta tells me that your PO was aware that the converter/chargers in these things were pretty lame and put up a defense against the worst (overcharging the battery(ies)).......that's a plus....
I'm a firm believer in "if it ain't broke, don't fix it"....so if it was me I'd be inclined to leave it as is....get a meter and monitor what is going on at different times......myself I'm going to install a digital readout meter right by the dinette table....won't cost much but I'll know where my batteries are at all the time.......but first, as I said earlier, I have to ditch my dead converter/charger as the charger part is not working anymore (just a little detail my DPO "forgot" to mention
)...not worth fixing.....that'll happen in the spring.....
and speaking of electrical
....I was browsing through "Crappy Tire" today and happened on a Coleman solar power
kit.....on sale! 50% off!!!....had to get it....forty watt panel with charge controller.....now I got more electrical
stuff to figure out.....LOL...Cheers from Courtenay and good luck to ya