Do the barrels sag in the middle?

Ken asked: Any problems with sagging in the middle of the barrels? With 400+lbs of water in each one it seems like they might. Any thoughts as to a middle support bar mirrored after the front/back supports?

Our barrels, after 18+ months, have not sagged. I recently had a need to empty one of the lower barrels and was able to inspect the upper barrel. Neither barrel appear to have any sagging or warping. I've seen some reports of barrels sagging on message boards, but ours have not. I try to rotate our water in the spring, and when I rotate this year I'll add some cross members in the middle of each barrel slot to provide additional support. I've taken a shot, looking up from beneath one of the upper barrels, and I could see no signs of sagging/warping.