Composite tanks are the ones I am building my propane locker for. They are light and corrosion isn't a problem. You can see the level of the propane in the tank. I have the mock up materials, the after market hatch and the tools set up in my shop. The weather has finally improved so I am spending my time on TD. The locker project will resume after the boats are on the hard. Ugh! The season is too short! I need a propane heater! Ha!