[PSUBS-MAILIST] My plans for a personal sub

Hi, I am a person that is VERY interested in building a small 2 man submarine capable of going about 50 feet deep in fresh-water. I plan on building it with a large propane storage tank, and using 2 car batteries, a trolling motor, a small 1.5 horsepower edger motor (with a snorkel for getting air and venting exhaust) for charging the batteries and compressing air, 2 regular size helium storage tanks for reserve air, and 3 variable sized tanks for ballast. Any advice you have is welcome and much appreciated, since I have very little experience with submarines but am anxious to learn more and build one of my own.