Sled, I’m not familiar with the marine storage practices your making reference to, regardless of the code requirements it comes down to how much risk will you take for a measure of benefit. I doubt there is any code enforcement, at least untill something goes wrong.
Gasoline is akin to black powder. How much are you willing to live with in the room next door? I wouldn’t mind having a lot of it, just not somewhere it will knock down my house if it goes off.
We all take risk, usually we don’t measure the cost versus benefit ratio. A person could pull out in front of other cars everyday and make the other driveer brake. That person might not get hit for years. The lives of everyone in both cars are at risk for 3 or 4 seconds of “saved time” If one day the other driver doesn’t brake lives are ruined trying save 4 seconds of travel time.
You can have as much gas in the garage as there is space to hold it, but at what cost if things go wrong.