I've got one on at the moment. I've had it for about three years and it's starting to rust away a little but it is to be expected considering it's position under the vehicle and what with the amount of salt that we've had on the roads over the last two years. I would strongly suggest that you plug the gap between the outer skin and the inner tank (you'll see what I mean if you look at the bottom corners). Weld them shut if you can and then coat the whole thing in plenty of paint and wax oil it when fitted. Water likes to creep into the seam between the tank and the outer skin and it'll rot the bugger away. Also, the six or so holes drilled into the top of the tank which are used to fasten the pick up pipe and the rturn pipe into the tank are wafer thin as opposed to closed and tapped holes which you'll find on the better tanks.
-Pos