Materials: Cardboard sheet/flattened box, Packing tape, Sharpie, Painter’s tape, Straightedge, Utility knife

Please watch the video, but these are the basic steps:

Tape up any slits if you’re using a flattened box to make it a solid piece.
Align a corner of the cardboard to the joint of the top tube and seat tube, and use painter’s tape to attach it flush under the top tube.
Holding the barrel of the Sharpie against the tubes, trace the inside shape of the frame, marking derailleur clamps, etc.
Use a straightedge to continue any lines where it was difficult to access (by chainrings).
Cut it out with a utility knife.
Test your template in the frame. There shouldn’t be any overlap or big gaps.
Fold up the template and put it in a mailer. Send me a message for my address.