Try Pacsafe products.
http://www.pacsafe.com/travel-access...rotectors.html
They do exomesh covers for your bags that you can padlock to someting secure. they do the exomesh and exomesh/bag packages.
I used an exomesh over a rollbag on the back of my Tenere, no problems and always felt happy to leave unattended.
Plenty of UK stockists to be found on the net.