In our case, if I decide to do the relay on the brake light switch, I think a better choice would be to tie into the 12 volt charge line coming from the coach. That way, if the coach is hooked to the towed, the relay is tripped. There would be no extra switches to remember to throw.
Bill & Denise
2014 Bay Star 3103 - 5 Star Tune
2016 Jeep Grand Cherokee 4X4 Limited