Our tanks are the 10 lb aluminum ones like this. They are about 16" tall and have a max diameter of 10.5". We bought the 20 quart aluminum stock pots that are 11" tall and have an inside diameter of 11.5". The tank fits in perfectly.
Matt bent some aluminum flat bar into the right shape to fasten the tanks to the push pit rails. He drilled a few holes in the bottom of each pot to act as a drain for any water that may get in or any propane that may leak out. A bungee through the top of the tank and over each pot handle and it's all secure.
And now we've got one stock pot/propane holder on each side of the stern. Safe, convenient, out of the way, and quite the conversation piece haha. That's it, project complete!