Chaotic,
I think I saw the same ones, green, 50 gallon, $13.00
I need something larger than the 35g rubbermaid I have and almost picked one up. However, I'm worried about it bowing out once its filled with water. The sides are flat without any rippling or other indentations which would give just a little more rigidity. My other thought was to get some of those seatbelt like tie down straps and add rigidity to it, or buy 2 and simply put one inside the other.
Also, read someone had a bad experience with some rubbermaid knockoffs fouling their fresh NSW. I think it'd be better off to get something more structurally sound and known not to fall apart from salt water.
Unless someone else here has used these.