I had a fitted tarp sewn with some military canvas I picked up at Sportsmans Guide. Rubber strap runs the perimeter eyelets. I've been happy with it so far.
I couldn't find my pictures, but they are in my signature link. When the equipment is removed at camp, I prop up the center of the cover overnight if it is raining to allow run off. While loaded water pooling is not an is not an issue as my equipment pushing up underneath the tarp allowing runoff. Absolutely no flapping at highway speeds. You can also see I had them fabricate a 5 watercan cover to keep the mud off of them in the tub forward position.
Dan