Here is my take on upright stand for MBP (13" or 15"). It is for later models - 18mm thickness. Design allowed for 1.5mm felt on both sides.

It is size that just fits Robox 3D printer.

Note: Complete version is updated as v2. Original was 250mm (by mistake) while v2 is now 200mm - exactly what is easily printable by Robox.

There are to options - print complete stand, upright, with support (I haven't done that, yet) or two arcs, two connectors and two distancers. Use one of arcs to make an outline on the paper and then transfer it to felt. Allow for distancer! (It is 10mm - 1cm high).

I have used simple UHU to glue felt to inside of arcs which I have roughen with a file before. If printing separate arcs you might need to use sand paper or file to 'adjust' connectors (and maybe distancer's inside) a bit.