gas tank question

[fm elliott]

I have 3 (6 gallon) metal gas tanks for a mercury outboard (2 stroke) on a pontoon boat. I want to put them into containers, or into the storage areas below the furniture. I have heard the dangers of tanks, venting etc. but am not sure what applies. I can install vents in either plastic storage containers or the boxes (below the furniture). Is there any specs. on how many sq inches of fresh air is required and how airtight it's safe to put a " good-dry" gas tank into.

Thanks FM