Hi James. Yes, It's tough scavenging odd parts in a small community. Like Dan said, if you used a common mild steel, and planned on replacing it later, that might be a better route. You could use a mounting method like bands or straps so you don't have to cut/weld when replacement time comes. It seems like you could coat the inside of a small tank fairly easy and increase it's longevity in salt water. Good metal prep before you weld it closed, and pour in a good epoxy paint. That's probably cheaper than stainless. How about an aluminum scuba tank ? a used one or two found on ebay would work, and the used ones that are too old to be used for scuba can be had for $20 each. They have 3/4 inch threaded holes so would be easy to plumb up. Frank D.