Use a 2mm metal drill to create 3 holes on either side of the platform.

Place one of the 40cm rails on the platform, 4mm +/-1mm from the edge.

Use a pencil to mark out where you are going to drill.

Secure the rail as shown with three M2 x 10mm bolts and M2 Nyloc Nuts

Be very careful with the carriage, either secure or remove them very carefully. If they fall off and are hit, the ball bearings inside them will escape!