I don't know what state the OP's Carrollton is in. But living in western NYS, if I leave out this time of year, it is guaranteed that I will be traveling over salt and sand treated roads and that much of that will end up on the underchassis of my motorhome.
Once I get far enough south, I head for a Blue Beacon Truck Wash that has the
Salt-Away Undercarriage Rinse. If I remember correctly it only cost a extra $5 on top of their normal $35 they charge for my 36 foot diesel pusher (some locations charge a extra 8%). Blue Beacon uses only warm, soapy water for all recreational vehicle washing and no acid washes. WeatherShield™ or RainX® Complete paint protectants are also available at a extra charge..
If I have to wait a hour or two in line, it is still well worth the wait, cause I want to get that salt off and the undercarriage properly taken care of.