Yeah, I think relays occasionally fail simly because they are relays.
I'll make sure to use dielectric grease, and I used waterproof tape to seal all of my temporary connectors on my original harness... which has like 3 times as many spade connectors as it needs because of reconfigs.
As for switching, I might be able to get a momentary double-ground between highs only and lows only, but I am almost positive that the FTP has seperate grounds so that it works when the rotary switch is in any position.