Best place for the 2nd battery is in the boot - yep in the rear of the wagon in a marine case.
Don't know about the shower unit.
Yes- you do need a seperate switch to turn the driving lights on and off. They may only actuate with high beam. Foglights also need to be switched and they become the main lights as you are supposed to turn the headlights off when these are on.
However, I do think there is a variation to this theme in Qld...