How about getting a pillion seat off ebay then bolting a Givi top box to it like I did with my R1, works a treat, is fully waterproof, easily removable and also gets plenty of looks !
France, Les Arcs camp site 10 day trip Padova, Italy via alps return through Dolomites lake Como, Kriega US-20 plus two 9 Lt canoe bags strapped to side, carrying tent and stove strapped on with Kriega straps and two velcro leg restraints ( long velcro straps ) travel light perfect no marks to paint work solid as a rock. Prefect
Ventura on the back and a baglux up front. Carry all you need and more. Went from Herts to west coast of Ireland and back last year, really solid kit and carries loads, costwise I paid around £420 I think for the Ventura fittings, pack rack, 2 holdalls (which double up as rucksacks off the bike) a waterproof cover and a grabrail when the packrack is not fitted. Can't remember how much I paid for the tankbag 8 years ago but it is a really useful item as well.