D B.
Mogas is good for about four months; after that, I would remove it from my airplane and run it in something that has an electronic engine control that can cope with fuel variation, like a modern automobile.
UL94 is basically 100LL without the TEL. Therefore they have the same longevity, as TEL does nothing for that aspect (it’s an octane booster, not a vapor suppressor or preservative.) It is about one year to be completely safe, but two to three years and still meeting specifications is not uncommon.
Humidity has a greater effect on your cam and other engine parts than it does on fuel, but after several years of exposure, fuel can suffer. My point is worry about short term humidity effects on your engine, not on your fuel, which you should be using up as noted above.
Hope this helps,
Dave