I want to install glass doors instead of a curtain on bathtub. The tub is from the 1940's and has a rounded lip instead of a flat lip. All the kits I have found utilize horizontal channels that need to be mounted on a flat surface. Does anyone know of a kit that can be installed on a rounded lip or if there is anything that I can insert between the lip and a regular channel to fill the gap and create a flat, stable surface?