We use the Rand McNally RV TRIPMAKER GPS 7710 for our needs. You do input your RV data and tow vehicle information into the unit. The unit will rout you accordingly to the input data you have provided. You can also switch between the RV and car/light truck mode and the routing will change accordingly. I have forgotten to do this sometimes and the unit will tell me I can not use this road surface and or a low over pass is ahead. The unit is thinking I am puling the trailer still.
2016 34RL CC; 2008 Ram Mega Cab 2500HD, 6.7L, 68RFE 6 speed, 4X4, Smarty S67, 100K+miles