Thanks for all your posts... I have got a better idea about what I need now - the Blood boxes that are transported by Bloodrunners have a strap on strip underneath so I just need a flat surface and something to affix the box to...
http://www.suzuki-gb.co.uk/accessori...=onroad&search
this suggestion is great but would be so much better if instead of those bolts to fix the topbox to there would be railings.
Any suggestions or ideas?