The upstairs tub is showing wear in three areas of the one piece acrylic unit. We think it's original to the house which makes it 28 or 29 years old. To save some money we were thinking of doing the work ourselves. BUT, when you stand in the tub you can feel three pieces of wood under the tub and that's also where the acrylic appears to be cracking. Does anyone know if that's normal installation and if it's an easy job to change it to a better installation? The floor is also large square tiles and I am wondering if they will crack easily when removing and replacing the tub.

Thanks so much!