I agree with Brian and for RV's that Garmin is great. I can clearly see it, it has non-glare screen and best of all it accepts GPX files that you make with S&T and download to the Garmin on your PC. This is so much easier than trying to find an address to go to in MX, and entering each point on the Garmin.
Never follow a GPS without first viewing the whole route and make sure it goes the way you want. It's capability of programming a good route is terrible at best.