Measure the ledge on the open side of the bathtub where you will place the door’s bottom track. Trim the door’s bottom track with a hacksaw to the length of the tub as you measured it. Run a file over where you cut the track to remove any sharp edges.
Put the track on the bathtub’s ledge where the track sits flat, leaving the same amount of space between the track and wall at both ends of the track. Place masking tape over the track to hold it in place on the tub’s ledge and mark lightly on the tub where the ends of the track sit.
Place wall jamb pieces on the wall above the bottom track, and then slide the wall jamb pieces down and over the bottom track so they lock together. Place a level on the sides of the wall jambs to ensure they are sitting plumb on the wall, and then mark on the wall where the plumb jambs’ screw holes sit.
Remove the wall jambs and the bottom track. Apply an even coat of silicone caulk to the underside of the bottom track, and then press it back into position on the tub’s sill. Drill pilot holes in the wall where you marked, and then replace the wall jambs.
Insert pan head screws through the bumper pieces, and then into the mounting holes on the wall jambs, and then drive the screws into the pilot holes in the wall. Measure the distance between the wall between the tops of the wall jamb pieces, and then cut the top track to the same length, minus 1 millimeter.
File off the rough edges on the top track, and then press the top track onto the tops of the wall jambs. Secure the hanging brackets onto the glass doors using blind nuts and machine screws that fit together through the mounting holes at the top of the door. Place the rollers on the bottom edge of the doors and drive machine screws through the mounting holes to secure the rollers to the doors.
Clean the inside of the top and bottom tracks with a rag to remove any debris. Insert the rollers on the inside door into the inside rail on the top track, and then slide the inside panel to the same end of the tub as the showerhead.
Insert the outside door panel’s rollers into the outside track on the top rail. Slide the outside door panel to the end of the bathtub opposite the showerhead. Apply an even bead of silicone caulk where the door assembly touches the tub or wall.