After we set up our barbeque to use the propane from the onboard propane system, we wanted to make sure that we had sufficient propane onboard when cruising. So we acquired a spare tank, but needed to store it somewhere. The side step on the transom seemed the right place. To keep it clean (no bird droppings, etc…), we sewed a protective cover for it from a white vinyl material. This also helped reflect the hot sun off of the tank.
To attach the tank we left an opening in the cover to allow a line to pass from the tank to the aft port stay. The cover is open on the bottom but has a cord that we us to draw the bottom opening close. It has worked well for the past three seasons.