I suggest you not limit yourself to finding a free app. There are several subscription apps that can do a good job of this. There are actually only a few routing engines out there that can even do rv safe routing. All of them charge a pretty hefty fee to the apps that use them. It is just not realistic to offer apps that can do this type of routing for free. Even ad supported apps cannot be sustained by ads alone.
I can recommend 2 alternatives, one is CoPilot RV, I have used this for years, it is not perfect, no GPS device or app is, but it is full featured ad reliable.
Another really good option I RVLIFEpro. This is a suite of apps that include a full featured trip planner, that can help you find campgrounds as well as select rv friendly routes. There is also a mobile app that can do real-time GPS routing of the trips you plan. Neither of these options is free, but I think you will not find anything that will do RV friendly routing for free.
There are 10 types of people... Those that understand binary and those that don't.
2018 Tiffin Phaeton 40AH/2018 Hyundai Elantra Sport Toad