I used the FRP panels and I like this stuff quite a bit because it is sooo easy to keep clean. FRP is not the least expensive option though...it MUST be glued onto something to give it some rigidity. I used 1/4 inch plywood, but I would probably would use 3/8 if I did it again. If you add the cost of even cheap plywood to the price of FRP (I paid nearly $30 / sheet in 2004), you will see that cost is not the main reason to use this material. Besides the low maintenance, I found it easy to work with around bends and curves, and looks pretty good too.

I would also say that furring strips are essential to prevent condensation from forming on any fasteners that you would use to attach the plywood to the metal trailer frame directly. There have been other posts about this topic in the past, but basically any screw heads that have contact with the moist air inside the dressing room should not attach to the cold metal trailer frame or else... condensation will "rain" down This is a main reason to use the furring strips: to bury these panel holding screws into, thereby insulating the screws from the the temperature differences in colder weather.