I pay a small annual fee for my Garmin's professional low bridge POI files. I get updates continuously throughout the year as new bridges are added. I can set the bridge height that I want to be warned about.
The file warns ahead of time (by my setting in the Garmin of how many miles ahead of pre-warnings) when a low bridge appears in our RV route. I would have to manually press the detour function icon for another route around the bridge - it's not automatic ... but then again my Garmin is not the model marketed specifically as being for RVs.
I wonder if the Garmin RV model includes the fully detailed U.S. and Canadian database so it can be used for boondock camping to - like we use ours for on occasion?