I'm with Jim E on this one. I use Microsoft Streets & Trips with a POI for low clearances. There are several with different heights and you can choose the height you want. Open the POI, plan the route, check to see if the low clearance icon is on or near the route, travel.
The Discovery Owners Club also has a MEGA POI database. It has just about everything you can think of in the MEGA POI file. Campgrounds, fuel stops, rest areas, state parks by state, etc.,
I have not found one for the MAC or iPad, yet. I use MS&T with the Windows Laptop for planning purposes.
Wayne MSGT USMC (Ret) & Earlene (CinCHouse)
2008 Winnebago Destination 39W
It is what it is, and then it is what you make of it.