Anyone having DEF fluid problems in a MB diesel RV?

AFIAK, each Mercedes service (either "A" and "B") requires the DEF tank to be flushed in order to prevent crystallization.

If DEF does crystallize/precipitate out, then I wonder about some form of agitation/stirring mechanism in the tank. Could be something passive that helps mix things when the vehicle moves, or active (such as the magnetic stir bar apparatus used in high school chemistry that has few moving parts and just a ceramic coated magnet in the mixture.)