Generator fuel additives.. yeah or nay

Our TH has a 30 gal toy fuel tank, and 20 gal gen fuel tank. I use the marine Stabil in every fill up, and since we don't use the gen often enough I run it once a month for an hour varying with no load, up to both 15K ac uits, and back down to no load. Also I fuel our lawn mower off the toy tank so I can rotate fuel quicker than just the gen uses.

So far so good. I have considered adding Marvel Mystery Oil to the fuel to help protect the steel fuel tanks, but I try to keep them full to help cut down on condensation buildup.