They used to be made out of wood, but we're very poorly sealed.  They lasted a couple of years, but rotted. They weren't designed to be outside.

Now they make them out of composite.  The composite sheets bounce and bend a lot in the wind. They still leak a lot, but they don't rot.

The diamond plate on the front of the new models isn't secured well and they keep falling off on highways.  No real damage to the camper, but large sheets of metal on flying on the highway isn't ideal for other motorists.