I have a North Face one – it wore out a bit after one trip, holes in it and stuff although that was a big 6 month trip and it got dragged around a bit / chucked onto several planes, on boats, buses etc.
For camping gear, assuming I have to carry it anywhere, I'd always prefer a rucksack – I've got a 75 litre rucksack, which can carry a 2 man tent, sleeping bag, thermarest, food and clothes for a week etc. The duffel bag is an absolute nightmare to carry when it is full, even for 2 people.
100 litres is massive by the way – you'd get a real load of gear in it. It is easy to pack though – just dump everything in without worrying.
If I don't have to carry it anywhere, i.e. car camping, then I wouldn't bother taking a fancy waterproof bag, I'd just stick it in any old bag / in the boot – you can usually pick up big bags from the market / cheap luggage shop.
The 100L one would be a nice bag for sailing + camping – although it'd have to be quite a big boat to have space to stick that big a bag in it.
Joe