The fiberglass tubs are so much different than a steel tub I really don't see how a standard steel bodied roll cage will fit in a fiberglass tub. A 1/4"-1/2" difference in the floor thickness from one leg to the next will throw off the cage quite a bit. I would say with any fiberglass tub the cage will need to be custom fitted to the body. The steel floors will give a little to pull it all together when bolting up the legs, but the fiberglass does not give it cracks.