We store an Atwood marine portable fuel tank (see below) with two Honda EU2000i's in our pickup bed, under a hard tonneau cover, in 119-degree weather in Phoenix, AZ.
Fuel tank swells up from pressure; but it does not leak fuel or fumes, because it is designed for this.
Important note: Our fuel tank is NOT stored with extended run fuel lines installed. The fuel fitting where an extended run fuel line would be installed is plugged with a brass plug.
Honda's do not leak fuel either, but they always smell a little of gas. The Hondas are transported in Rubbermaid Action Packer heavy-duty tote boxes with weather strip seals added around lid. Fuel smell is confined to inside of storage boxes.
I agree with comment on using fuel stabilizer for fuel saved more than a month or so. It's probably a good idea to either use up the fuel after a two-week vacation (put it in your TV or car) or just add Sta-Bil every time you fill the portable fuel tank. See link below.
Attwood 6-Gallon Fuel Tank - Walmart.com
ActionPacker® Cargo Box / Bin | Rubbermaid