No one above seems to be aware that "sealing off" the bottom of the propane locker is NOT the thing to do. Since propane sinks in the atmosphere, it creates the hazard of its leaking into the bilge, where a spark could blow up the boat. This is why CNG is considered preferable, because it rises, and will then dissipate into the atmosphere with no danger of explosion. If the bottom of the propane lockeer is sealed off, any leaking propane will end up filling the locker, just waiting for an errant spark to set it off. Propane lockers should have bottom drains leading overboard to a point above the waterline so any leaks will definitely go overboard and not into the bilge. CNG is much safer and easier to work with, but is a lot less easily available, so most installations go with propane, but follow the rules carefully.