Our 5th wheel is 13' 4" actual measured height hooked up.
We traveled FT g=for 7 yrs. using backroads/secondary roads majority of time (hate Interstate travel)
Didn't use GPS etc. Didn't worry about it.
Only came across 2 bridges/trellis that were NT marked long before coming to them (most were marked far enough ahead to allow for alt. routing).
The 2 we encountered were 10' height range. We either missed the signage, signage was missing or overgrown......we just turned around and went different route. Part of the travel adventure.
Most height issues are within CGs........low trees etc.
Gotta look UP!