I have used the Rand RV GPS for almost 18 months and over 35,000 towing without too many issues. I will caution you that all low overpasses are not entered into the database.
I run two GPS units on my dash when towing, mainly because I program one for fuel destinations. I also consult my Trucker's Atlas the night before. It only takes a couple of minutes to check the next days route to make sure there are no issues and if you purchase a Trucker's Atlas every couple of years you will have all the current information you need.
No matter what GPS you are using, never trust them 100%.