passport america trip routing

I have been a member of PA for 10 years but never used their trip routing so have no idea of its worth. We do use the Truckers Atlas available at most truck stops to verify if a road is compatible with 18 wheelers. If so we will certainly fit. The problem with it is that on many roads, especially near population centers, 18 wheelers are prohibited whereas we are not. We also have a RM 7720 GPS which, so far in three years and 10,000 miles) hasn't routed us on a road that couldn't handle us. Though there are some exceptions we have found that most US numbered highways are OK for us. We use a combination of these items as well as Google Maps/Earth to check our route before each day's trip. Knock on wood, so far we haven't gotten into a situation requiring us to unhook Libby to get out of it.