Contact a local marine supply dealer. You can use the same type of paint that is used to paint a fiberglass boat. The paint is considerably more expensive than house paint, and the actual painting project is not easy-the paint should be sprayed on for even coverage, so not an easy job for a novice to home improvement projects. In the long-run, however it may be less expensive than a new shower or tub. If you are close to a marina, you may want to find out who they use to paint boats-perhaps you could contract this person for the job (especially off-season). Likewise, you may also ask an autobody specialist-they could prove to be very informative on appropriate paints as well as the possibility of knowing someone who can do the job if needed. Good Luck!