I use a Weathershield car cover, and after a recent rainstorm it left some smudged mud on the top.
I tried scrubbing w/a sponge and soapy water; also tried 303...still have a few smudges that won't come out.
Any suggestions?

 

I would try rubbing the area with a little carwash shampoo with a toothbrush dabbed in water... then treat it with 303 vinyl cleaner then protectant

 

as moonsurfer suggests a brush is likely your answer.
i would use a bigger brush (like a wheel brush) but a toothbrush might work too...
scrub the area with some elbow grease and a good shampoo (you can use a top cleaner)- and report back

 

Okay - I'll go over the spots with a toothbrush and we'll see what happens.
Thanks!