Good thread, from my own experience the snap on vinyl ones with no support collect rain water and sag in if you park outside and it rains or snows on them.
I want a Gaylord cover for my truck and then plan to cover that with vinyl top material or convertible top material but due to the cost may make my own similar to what has been described and cover it with the material.
Early 90's Dodge Grand Caravan rams are pretty easy to get and should hold one of these covers up pretty well. Here at O'reilly's they are 19.99 each new.
Denee the aluminum angle can be found at metal supply houses that sell aluminum pieces. There should be a number of them in the Houston area that do. Big issue with that is that most of us don't have the equipment to weld aluminum at home. It can be gas welded but that takes some practice. here is a yellow page listing of possible sources in the Houston area
http://www.yellowpages.com/houston-t...num-angle-iron some may not sell to the public though.