Maybe some sort of rain deflecting anti gravitational force field around spark plug three
In fairness it's not always practical to put a full cover over a bike so a small guard to deflect water away from the spark plugs is a good idea
I'm surprised it doesn't get mentioned much more often to be honest, as there are plenty of people that don't garage their bikes overnight.
Mine's left out in the elements on a daily basis, but not 24/7.
I used to use a cover at work but taking it off and storing it when it's chucking it down became a bit of a chore so i haven't used it in ages.
In Bretty's case i would make sure the drain hole is clear, give the area around the plugs a blast of air occasionally then just cover it with WD40 every now and then.
Changing a plug every 6 months sounds very excessive to me.
Or the more expensive way is to consider an extension of the fairing.