Definitely ACF50! All Weather Biker did a great job on my K12S which sat out on the drive under an Oxford and various other covers down the years. It wasn't used to commute but got used all year round as and when the fancy took me.
I actually took all the panels off before taking it along to a public treatment session but the guys had really long lances to get into the engine bay and all points south and I needn't have bothered.
If you do it yourself then make sure you cover your tyres with sheets or take the wheels off; there's a vid on Utube of a guy slathering it all over his GS and then riding off with the tyres smothered in the stuff. I guess he survived as he posted the vid but I'd be more cautious
Oh, and make sure you have a decent security set up...