Hi Pete,
Thank you. I created the green mail slots by glueing a flat row of "Plastruct ST-4 traditional ABS Square Tubing" side by side. Once the first flat row dried, I cut off the backs and they looked like the bottom row of mail boxes. From there I glued another row of ST-4 on top and repeated the process until I got the height of mail boxes needed. It took the whole bag of ST-4 to create the effect. It probably would be easier if you know someone with a 3D printer.