Never store propane inside your cockpit. Propane is heavier than air and WILL seep into the cabin. Mounting the tank on the aft rail would be much better EXCEPT that the tanks really don't like seawater and will corrode to junk unless you have one of the fancy new glass wrapped composite tanks.
Exactly my point. I'm not seeing an easy way to resolve this. I'll search the forums, but it looks like anchoring and starting a campfire on shore is a better option at this point.