Make sure that the shower tray/bathtub is level.
Measure the back wall and the two return walls.
With a hacksaw, cut and miter the corners of the base profile.
Use shims (Fibo Sealing Tool) underneath the profile and dry fit the three pieces.
Apply Fibo Seal behind the base profile, make sure it’s level.
Leave a gap of 1/4 -inch between profile and tray, and screw into position.
When using Fibo in the whole bathroom, follow the same steps, and leave a gap of ¼-inch between the base profile and the floor.