By Pass Shower Doors

I want to install a by pass shower door with my Sterling Vikrell 3 piece shower unit. What type of screws should a person use to install the rails onto the fiberglass, or would it be sufficient to just use silicone. I am concerned that I will not find any solid material to attatch to behind the fiberglass unit. Thanks!

The only screws you need are those to attach the jambs on each end. The bottom rail is just caulked to the rim of the enclosure or tub. There should be installation instructions with the door unit.