Check out Steve at Better Boat Covers, 916-421-1819. He modified my old cover to work with my tower, and it's so tight that I have towed with it a few times already. An added bonus is that I can now cover the boat if I leave it in a slip somewhere. It's a bit of a drive to sac, but he does really nice work IMO. He also made a really nice bimini for me, but I don't have any pictures of it with me.
He's friends with Rick H (Blastmaster), which is where I got the referal from, his name might get you a discount of some sort. I paid just under $800 for the creation of the bimini, and the mod of the cover.