Thanks for the info guys,
I decided to build some myself. The custom tank companies are building them out of 1/8" aluminum. I decided to use 12 guage as to save on wieght. All together, the material was about $200.00. One tank is almost done. This thin of material is not easy to weld, but the tanks are only about 5 lbs heavier than the fiberglass ones that I pulled out.