I made a firewall for RC planes. You can glue one side to the plane and screw the other to your motor. It's 49.5x44x2mm on one side and 2.2mm on the other side because of one motor. the holes aren't perfectly aligned because my motor mount also came a little bit crooked. I also haven't added all screws in for the motor but ignore that. :)

Hope this will help, for print settings I forgot but do what you think is the best.