We've been using the Rand McNally GPS from Good Sam for the past year. It's specifically designed for RV's, and it allows the user to enter the height, length, weight and type of RV. It gives you speed, curve, hill, work zone and clearance warnings. I also have in-dash navigation, but that unit frequently sends me on routes that I wouldn't want to take the trailer on!
2014 Dutchmen Voltage 3905 Epic III
2008 Ford F450 CC 4X4 6.4 4.88's, B&W Companion Hitch
2011 Jeep Rubicon Unlimited/2004 Polaris Sportsman 500 4x4