Made this for a polystyrene window insert (30mm thick). Printed with Fillamentum PETG. Nozzle size, layer height or infill don't matter too much.

Hardware:

• 4x countersink M3 screws, ≥5mm long
• 2x countesink M2-M3 self tapping screws
• 4x M3 heat set inserts (optional) | TME link

The door itself can be cut out of a flat piece of a suitable material. Use the holes in the sides of the frame to loosely screw it in place.

You can avoid the need for the threaded inserts and screw right into the plastic, when assembling the frame. Use the 'self-tap' file with undersized holes for this.