These will work to keep the water from standing.
http://www.saveonpoolsupplies.com/shopp ... ool_pillow
I have a full cover for my 21SC made from Sunbrella, and yeah it can be a pain to deal with, but you can leave it off for the times the boat will see frequent use. Those cheap tarps just don't last in the Florida sun.
When it comes time to replace my full cover, I'm thinking of going with something more simple, again made with Sunbrella (still need to keep it hosed down with 303). Anyway, I'm thinking of sinking some 4x4's near the boat and either making or modifying these for easy on/off doffing and storage of the boats PJ's.
You can go to a local upholstery shop with your dimensions... if your not choosey about colors, buy your sunbrella knock off brand on ebay. finding nylon zippers might be a challenge. Or if you can sew, often you can buy an antique tredle sewing machine to use. It's my understanding these machines will punch through almost anything and can be had ofter for less than $100. You will also need to add your own gromments for proper drainage, depending upon your design.
http://www.saveonpoolsupplies.com/Pool- ... olar-Reel/
No doubt a little shopping around will find lower prices on either of these items.