The Ford keyless control module should be behind the panel immediately next to the door on the right side of the step well when you enter the coach. This just below the dash. The module will have the code on it.

My 03 H-3 has a master chassis disconnect switch near the ignition key. It should be off when the coach is parked. It's also a good idea to have an intelligent charger on the chassis batteries.

You probably have eight 4D batteries over the drive axle for the house bank. If you don't try camp, you can reduce your bank size to four 4D batteries. Featherlite makes this easy as they should have each battery directly wired to buss bars. You can take two out of the 12V half bank and two out of the upper or 24V half bank.

Your flickering house panel lights when turning the DC switch off could be due to a capacitive effect in the switch controller. I wouldn't worry about that. It'seems a good idea to turn your Trace inverters off before removing the AC or DC source, but it shouldn't hurt them if you don't.

Once a battery's plates get exposed the battery can do bad things, like grow or even explode. Chassis batteries are generally maintenance-free flooded wet cells. In the heat they will still lose some electrolytes.