Thanks for the ideas guys, my search using the " search" button came up trumps.....
I found this thread, yes I know its on an 800 but you cant have it all, good photos and good ideas for mounting, all in all a bloody good thread
http://www.ukgser.com/forums/showthread.php?t=218935&highlight=Peli+case
Ive measured a 45 ltr givi box and the dimensions are..
500mm wide, 400 mm high , and 250mm deep
So I went on ebay and had a look at the cases that were on the 800gs in the first thread and found this...
http://www.ebay.co.uk/itm/DURATOOL-..._Tools_Tool_Boxes_Storage&hash=item3a6c26bb72
As you can see they are just a tiny bit smaller so I would say a 41 ltr but the best thing is the price...Totally waterproof and ABS plastic, perfect just bloody perfect...Thankyou to all.....Tosh