Side mount boxes now available for both oil cooled and liquid cooled GS/A models. Box is welded, with a gasketed door, and mounted on the pannier frame. Sells for $199 plus $15 shipping in USA, includes all mounting hardware. Check out current boxes at www.advgear.net-
It is necessary to remove the crud catcher, it'll hit the box when the suspension compresses.
More photos and install info on the advgear.net site
Fill out contact info on website to order.
Right hand mount for pre 2014 oil head bikes:
Left hand mount for liquid cooled 2014+ GSA or GS with OEM pannier frames: