Might want to consider putting a vent at the bottom of one of the side walls of the gasoline storage shed to prevent the buildup of gas fumes which are very explosive.
Gasoline fumes are heavier than air which is why the vent goes at the bottom—probably would want to screen it in some way to...
I redid two trailers using the wire brush/sand/rustolium rusty metal primer and rustolium topcoat you describe in option 4.
I used the Rustolium “Hammered” finish for the topcoat (put on two coats) and both trailers came out looking good—-the hammered paint covers well and hides the surface...
