No...or at least I don't notice any rub
It's easy to take on and off the bike, just three straps. It's not as fast as clipping a pannier onto a rack, but as it only takes 30 secs I don't mind. I will often leave the bag on the bike over night.
Tire rub can be an issue when not using a support and it's vital to pack the bag tightly so that it doesn't droop. Also the buckles of the mounting straps need to be inside the bag so it can be tight against the saddle also minimizing droop. I have a 56cm bike and have 2cm clearance between the bag and the tire.
The Carradice Camper longflap weighs 2lbs, which isn't good. I have a Carradice Overlander saddlebag that is as big, made out of nylon and weighs half as much......but there's no longflap so I prefer the Camper.
Good to know. 2 pounds really isn't bad if you back out the weight of a rack (maybe 700 or so grams). The camper long flap is positively svelte if you use this as your baseline.
The right comparison would be a rack with really lightweight bags (say the Arkel dry lites). This gets you to 1200 or so grams (assuming a 700 gram rear rack) (the camper long flap is 980 I believe) but you end up with more storage space (the Arkels hold 28 liters and you gain the top of the rack for that wet tent. That's not a bad trade off and the arkels plus lightweight rack might be the way to go. The tubus fly and arkels get you to 900 grams (less than the Carradice) with more carrying capacity.