The sales person was correct. Especially if the switch is mounted horizontally. Water can pool at the bottom and cause a short. I sealed my switch so that water cant get into the contact bolts inside the switch. Hopefully that will do the trick.
Retired Fire Dept Battalion Chief
2016 Ever-Lite 232RBS
2012 F150 FX4 W/Max tow & Ecoboost (Best tv ever)
2018 F250 Lariat (ok but I miss my F150)
Getting old ain't for wimps!!!