These are pretty cheap and easy to replace. That would be best.
If you still want to try and clean mix 1 part Bleach with 1 part Mean Green and add a few squirts of Dawn. Spray on with a squirt bottle and rinse. Do a test spot to be sure it will not damage what you are working on before doing a large area.
This is the only thing I found that would clean the white soft rubber window molding on a previous camper.