Cleaner for the white around windows?

Why not just replace??? I got a roll for around $60 bucks that did most of ours (small trailer) Just pulled out old and put in new. Cleaned out weep holes etc.. when at it. I used a heat gun to get plastic warm to stretch a little bit at corners. Yours might be different type but when all done, I wondered why I didn't just replace them a lot earlier. Mine were not that wide either.
In this vid you can see how they come out and in. http://www.youtube.com/watch?v=ZBL3pvZ8kGg Hope this helps.

I use Acetone to clean the surface of windsurfing sails I am repairing.

Product name is: Acetone Dupli-Color Premium Cleaner; CM-521.

"Cleans unpainted fiberglass surfaces;
Removes grease and wax from glass, metal and wood;
Evaporates quickly, leaving no residue"

Use caution with the acetone. It can melt some plastics and can remove paint. It will also damage fiberglass. You might try a chlorine bleach base cleanser. It will most certainly kill mildew.

I had some success with off the shelf mildew cleaner, don't remember the brand. I didn't keep at it on a regular bases and it came back after a time.

OK, thanks.. I tried the OxiCLean scrubbing bubble stuff that goes on blue and turns white when its 'clean'.. and it wasn't.. at all. I scrubbed with a sponge that has the rough side and it did make a small improvement.. but it was lots of effort for very little reward.

I tried "pure Citrus" organic cleaner as well.. no dice.

Don't have Acentone here.. will research that a bit and see if I should pick some up.

or Oxyclean

Read somewhere that Acetone is the stuff to use!

Try Clorox clean up and a 3m scotch pad. I have also heard magic eraser works.

Whatever you do, I'd be careful using anything too caustic on the seals because they are rubber gaskets.

It looks like regular old mildew to me so you might try some scrubbing bubbles or similar products.

WoodGlue