I helped a guy move a 21 year old HS a couple weeks back that had some damage on the bottom in a couple corners but not to bad, he was able to fix it pretty easy. Tore out some foam before we placed it and had it on the dolly and cut in a couple 2x4's
With proper drainage on your base any tubs base should last the life of the product. Alot are useing plastic or fibreglass bottoms, this helps but may be unnecesary overkill.
