I'm not singling your post out here, Mark, as you're not the only one to discuss the potential issues with the stability of gasoline.
This is very unlikely to be the case unless either:
1) water got in
2) a lot of vapour got out (poor seal and major diurnal temperature variation - and a proportionally large loss of the light ends)
(and both the above are compounded by smaller liquid volumes / increased vapour space in the tank)
The stability of gasoline is sufficient so that a single winter of weathering in all likelihood won't result in a major change in fuel quality. The temperature range Rob descibes, if repeated, may account for a slight loss of light ends, but the rate decreases with time as the RVP decreased commesurate with the loss of light ends.
Regardless, and again as Rob alludes, water ingress is the primary concern, as opposed to the slight increase in IBP. At worst, the bike will not run smoothly on account of the change in fuel quality over one winter, but won't run at all on water
However, I don't have personal experience of using stabilising additives, and have no recommendation to make in this regards.