I like the tube material (sealed on two sides) available from ACP or CST. They also sell clips to close the ends with. I first bought a 36" wide tube but switched to the 18". I almost always get a very good seal and it is faily easy to get the wing into the bag and then seal the ends with the clip. I think ACP sells it for 4.25 for 3 yards, fairly cheap and I can reuse it numerous times.

www.acp-composites.com
www.cstsales.com

good luck,

kevin