About a year at most with a storage additive is about all you can expect . If exposed to the high temps, the gas will lose too many of it’s lighter ends. 100 degrees for any extended time will significantly reduce storage time, probably in half. I have stored gas here in Alaska for up to 18 months without problems, but it doesn’t get any where near 100 degrees.
I’m in MN, 100 is rare, but not unheard of. I’m thinking more of what the temp gets to inside the shed.
Maybe I’d be better off just filling an extra, rarely used truck. Storage tank on wheels :)
Even in a hot desert, the temp stays cool and even 4-5 feet underground.
If you can dig a hole and keep it well covered, you can get better storage conditions and great safety. Just be sure to call it a shed, as underground fuel tanks have special restrictions.
Plain holes in the ground can also flood, so keep fuel watertight, and off the ground to avoid rust. DIg a little deeper sump on the side for water to drain into.
If you have anything larger than a five gallon can, like a 55 gal drum, you might also need a pump, as siphons won’t work if the source is lower.
Fuel stabilizer and rotation of the stock is necessary with gasoline. Diesel is a little better and propane is practically forever.
I routinely store non-ethanol gasoline for two years and then rotate through vehicles mixed at about 1:1 with new gas. If 100% stored gas is run then there will be pinging under load. So I don’t do that except in an emergency or I add octane enhancer (does seem to work).. Stabil is added at the beginning; some containers are plastic, some metal The plastic containers lose much more due to evaporation. Temperatures in the storage shed range from -20F to +110.