We have fiberglass pits because in drought years our flood water has some salt in it. They are just ok. Not nearly as durable as steel. They tend to leak frequently and the leaks seem to be harder to stop than with steel. Yes they are lighter and easier to move, but practically I think that if I tried to dig them up they would tear up and have so many leaks that they wouldn't be usable. Go with steel if you can. With our salt problems, aluminum is what I would go with if I had to redo.