we installed an acryllic tub insert and walls a few years ago, and were told not to use a cleaner that could scratch the surface. but nobody is willing to give us a preferred brand or type of cleaner that they recommend. do you know of one? also, you mention to use an automotive wax on fiberglass walls. is this the same for the acryllic systems? don't some automotive waxes have some ability to scratch the surface as well? or would something like Nufinish or a basic Turtle Wax liquid be OK?
A simple solution of water and liquid laundry detergent applied with a sponge is a good way to clean fiberglass walls. Also try a paste of baking soda and water for stubborn stains and grime. For acrylic, yes car wax is ok – test a small area first and follow all the manufacturer directions. Avoid using it on the floor of the shower as this could become slippery. Also some have recommended toilet bowl or other soft, gel household cleaners. Good luck!