I've been looking for something to stick on the GS to carry items ie, camera, cigs, spark plugs, etc. Found this tail bag at a local shop and love it.
http://www.imotorcyclestore.com/cgi-bin/dpsmart/products.html?L+ims+otgx2185+_DCatNum_02S11BIKTBA_01PageType_02L_01
I paid 50.00 for it. It has 2 bungees that run through the bottom of it and they clip to the mushroom under the seat. Perfect fit.
Just thought I'd share the info.