You can always use a Blue Beacon or other truck wash. Around $65 for my truck and trailer at Blue Beacons. They follow directions well, and we have never had water get by the slides or in the wATER heater or furnace vents as we ask them not to spray them.
Elliott, Vicky, and Sadie, our GSD
2014 Redwood36RE Titan Disc brakes, 17.5 " Sailun Tires
2013 RAM dually, CTD, Aisin Tranny, CC, LB 4x4