Mark-



If it's an acylic tub are you planning on using something under the floor of the tub to help take the weight?

I think that when Rico said this he wasn't concerned about the weight
of the tub or water.

IMO he was concerned about the flexibiblity of the tub bottom.
When a person steps into the tub, unless the tub bottom is well
supported (wood members, well spaced or lots of foam) the tub bottom
will flex downward.

It's a minor annoyance but can also lead to premature flexural failure
of the tub by cracking; cast iron doesn't have this problem.

cheers
Bob