just get a one piece rainsuit to go over your regular gear. with wet weather gloves and boots or covers for the boots. you'll have plenty of luggage space
to carry it when you aren't using it
oh and since i didn't get the ST4 you have to create some half fairings and build the bike i wanted to do
+1...a real pain in the arse to get in and out of but relatively cheap and very effective, used that arrangement back when I had no car and rode year round it worked well, kept me warm and dry in really bad weather.....