I fitted straight NGK Spark plug caps.I don't ride in the the rain unless caught so the little rubber skirt I made out of some old inner tube does it's job ,
However if I was going to use the Bike to commute I would make another bigger piece to go over it as added protection.The engine doesn't get hot enough to cause any trouble to them,even stopped in traffic.I know this as I quite often check my Spark plugs.
I do have a,"Fender Extender" fitted as recommend on this and other SV forums.
Just some thoughts