Good Gosh, fabrication isn't rocket science!
George, about a boat buck ($100 here in the South) and a weekend's work can make you a happy camper if you are having this much trouble finding a tank and have some basic DIY skills. Remove your tank, use a skill saw with a metal cutting blade and remove the top leaving a 2" flange all around. Use a metal cutting hole saw in your drill to cut out all of the fittings.Using filled epoxy repair resin make a concave fillet at all inside corners with a tongue depressor. Using epoxy laminating resin (never polyester) and fiberglas cloth, fabricate a new tank inside the old one, three layers should be adequate. Be sure to roll the laminated cloth back, over, out and on top of your flange and a little beyond the outside edges of the tank. Fabricate a new top, a little larger than your finished flange, on a flat surface covered with polyethylene sheeting as a mold release.Next day, use a hole saw to cut holes for your fittings. Use the metal tank cutouts as a guide. Epoxy in (or use 3M 5200 unless Peggy objects), from the inside out, new flanged replacement fittings (this is a good time to move up to twin 3/4" vents and relocate for a less obstructed flow if neccessary. Don't cheap out and use the old aluminum fittings). Consider installing an inspection port in the top at this time, there are pros and cons. Trim the edges of the flange to the sides of the tank and the top to match. Then, sand the mating surfaces flat. Using the filled epoxy resin, bond the new top to the tank flange clamp it or weight it down until cured. You can reinstall the 'new' tank when cured.Follow the mixing instructions on the epoxy carefully, a proper mix is critical to a good cure. Pre-impregnate your cloth with the epoxy resin before placing it in the 'mold'. Roll or brush out all air bubbles during the layup but don't starve the cloth of resin. Use protective gloves, eye and respratory protection.If you want to use the Snake River HODA sensors, cut out a large panel on the most accessable side, 1/4" from the top and bottom and 6-8" wide. Cover the panel with polyethylene sheeting and tape it back in place with duct tape. Be careful while rolling out the resin in your laminate in this area, you'll have to hold the panel in place or rig a clamp. After the laminate cures, the metal panel will pop right out and you will have a nice smooth, flat surface to apply the Snake River foil and sending module.Some people advocate using this process to glass in the entire locker where an old tank was located in order to maximize tankage. Personally, I think that this is a very Baaaaaad idea. Good luck and have fun.