Any question answered...

No experience of Humps but if it's waterproofing you need just buy a cheap dry sack from a camping shop and stick that in your rucksack (you can go full on rubber but they are bulky or you can get one of the thinner more 'nylon' ones). I get the impression the Hump covers are all about visability rather than protection from water.

this sort of thing?

http://www.kathmandu.co.uk/Packs_&_Luggage/Organisers_&_Accessories/Protective_Covers,_Cases_&_Dry_Bags/40417/Dry_Sac.html

interesting, cheers for the advice. yeah interested mostly for waterproofing although hi viz is probably a slight plus too. when i'm driving i find hi viz stuff more visible on cyclists than lights. the dry sacks are cheaper as well though so thanks for the tip - will check one out in store.