Oh yes! The best you can buy is the British Army bergan. Its 100 litres as standard, but has two zip on pockets that take it to 140 (i think). Theses pockets can be zipped off and turned into a smaller stalking sack. These are 100% waterproof, super tough, green or cammo, will outlast ANY of the fishing ones available, and will cost from about ?40 for a used one in good condition. Try http://www.transworldsurplus.co.uk/rucksacks_holdalls.htm or call them on 01788 333566. They also do some of the smaller engineer and medic ruck sacks too. All worth looking at.
Andy, I've managed to do my back in 'again' so will be using my barrow from now on. I have the Fox Ruck Box, about 2 months old, used probably three times just sitting on the wall in the garage. If you want it for a fair price, then give me a shout at stuartdennis@msn.com