
I built the strip using two layers of styrene. The first layer is thin: .04 thick. The top layer is .08. That brings the total thickness to just under the required .125. With primer and paint, the strips will be just thick enough.
Making the strips is very simple. Just cut the two rectangular pieces, glue them together, and after they have dried, file one end by hand to give it the correct chamfer. Use lots of glue, especially around the edges.