You would think the vinyl trim industry should be looking for some kind of answer since this is a known problem. 
I will try sanding it smooth to see if that helps. That would make sense that if there is less for the dirt to grab onto, it should stay cleaner. Guess that is the same theory as using the acetone to close up the pores. Maybe sanding and acetone combined will help. The factory edges do seem to stay much cleaner.
Painting would solve the problem, but one of the primary reasons for using vinyl was to eliminate painting.
Thanks for the info and replying.
I will try sanding it smooth to see if that helps. That would make sense that if there is less for the dirt to grab onto, it should stay cleaner. Guess that is the same theory as using the acetone to close up the pores. Maybe sanding and acetone combined will help. The factory edges do seem to stay much cleaner.
Painting would solve the problem, but one of the primary reasons for using vinyl was to eliminate painting.
Thanks for the info and replying.