Maybe it's different where you are, but here, this would be a nonstarter, for no reason other than there is probably a prohibition against it in the local municipality's codes.
The issues you need to evaluate are: (1) gasoline, (2) by a lake (water), (3) underground storage (hard) or aboveground storage (probably dangerous), (4) dispensing of motor fuel.
I completely disagree that this is anything remotely like storing fuel oil. The volatility of gasoline means that even at 100 gallons you are putting a potential bomb on these people's property. The idea of storing it out in the sun in and of itself is likely an issue. The idea of storing it near a public water area is an issue. Here, the DEC tells people they can't build a 4x4 wood lean-to near the water. Gasoline tank? They would laugh the propertyowner out of the room. And if someone just "went and did it" without the proper permits, they would drop fines on the propertyowner and anyone who helped them that would be financially-ruinous for many years to come. Again, it may be different where you are.
However, if you manage to navigate the legal thicket, I know we would love to hear how it all works out. In the meantime, the suggestions of alternatives that others on here have recommended are the kind of suggestions that should be taken seriously.