I have the Garmin RV 660 GPS.
It allows you to set up and pick the various vehicles such as car or RV. You enter what the specs are for the unit you are towing such as height and length. You can then select car when you are not towing and RV when you are.
It works rather well but tends to want to wander off main roads to back roads. It has lifetime maps but the update process is very painful. I started the update yesterday at 1pm and it finished sometime this morning. Very slow!
Regardless of whatever GPS you choose it is a good idea to try and review your route before hand or you could find yourself in a tight situation.
Dave
2013 2500HD Chevy LTZ 6.6 Diesel Ext Cab Long Bed
2017 Grand Design Reflection 27RL 5th Wheel
Dear Wife, plus two Cocker Spaniels and a Standard Poodle