You can install a fiberglass shower base with a little preliminary planning and preparation. Premade shower bases allow you to essentially drop in a floor for a new or updated shower without a lot of concern for leaks and plumbing issues.
First, you should have removed the existing shower base or tub so that you have clear area for the new installation. You will want to insure that the floor and underlying material is in good shape. If not, now is the time to tend to it. With a clear space, make sure that your available area matches with your shower base. The old adage to measure twice and cut once certainly applies.
If you are running new plumbing you will need to mark the space for the drain hole. You can set the shower base in its spot and mark out where the drain plumbing needs to go. This will allow you to run proper pipes to the exact drain location. You should check local codes on the requirements for venting your drain. Make sure your drain is properly installed and has the proper grade before closing up the floor. You can then set the shower base in place.
At this point you can insure that the supply lines have been stubbed in and are properly lined up. As you position the base, you should shim any area that are not level and properly “shored” up. Having a level base will insure good drainage so confirm that it is done correctly. You will want to permanently install the base with an appropriate mortar. This needs to cure for approximately 24 hours depending on what you use. You will have to confirm based on the exact mortar mix you use for you shower base.
Finally, you can install the drain cover and gaskets. Use the included directions for your particular drain hardware. Not only does this keep the water out of the subfloor, but it finishes out the smooth floor of the shower base.