The Hein Gericke roll-bags are very good bits of kit.....they also do a large selection of other stuff,such as bergen/rucksack liners and pannier liners in a multitude of sizes.
Hell of a lot cheaper than ortlieb,and still robustly made.Not as heavy-weight as the ortlieb stuff.....but i prefer that,im used to having to carry my camping stuff about in a bergen,where heavy-weight doesnt tend to best.
Hein Gericke are also doing a lot of useful carrying equipment add-ons,such as a bag for fitting to your headbutt pad on the handlebars ( £8 )...a bum-bag with a built in toolbox section,and a tank-bag system with over-the-side panniers to drape either side of your fuel tank ( £65 ).....with a few well placed straps,i reckon they would fit my 1150 GSA.