Re: plastic boat cover (Stamoid)
I agree with the above (not that it sucks, but there have to be steps taken). I've been the business 20 years and I only work on Stamoid after the customer insists on it. You will wind up with little black mildew spots on the underside. It's not usually visable from the topside, but even after bleaching, they come right back.
Aside from Sunbrella Plus, you can also look into Top Gun material as well as Sea Quest. Beware tho, that any material with a plasticized backing is going to shrink up over the next few years more than standard canvas, so have the shop be a little generous with your snap settings.
If you're set on Stamoid, make sure they stitch 'clamshells' into the cover so it can breathe.