Metal rails steps
Remove protective foil from plate. All holes need to be widened so that top parts of srews will sink in evenly.
Try to fit rails into the plate. They should fit snug into the plate. If they do not, this can be because the inner angles of the teeth in the metal rails might not be sharp enough. File them into sharp edges with a plane metal file until they fit.
Try to fit rails into the plate.
File the corners so that the rails fit snug into the plate.
Glue rails to base plate
Apply epoxy glue to all areas that will be glued together. Set rails into base plate.
Set rails into base plate.
Put top piece on the rails to fixate them in their correct position.