Don't have a motorhome and don't have DEF- so take my response with a grain of salt.
But, with my diesel truck when I'm traveling the highways- I solely use truck stops and go around back to the truck pumps. They've almost all have DEF pumps either at every pump or at clearly marked pumps.
When you pull in, just make sure that you leave enough room for the door to swing upward between you + the barriers/pump/etc.
The only concern/question I might have is which side of the motorhome is it on and does that pose any unique challenges with these DEF pumps? And/or how close to the fuel tank filler is the inlet? I didn't pay enough attention to know where they were located.