A couple of stacked sheets of foam board (sold at Staples) cemented together will take and hold pins very well. They do not have to be very large. You might try something like 24 x 10 inches to start. That will let you build many wing sizes for small planes. It is important that the underlying surface supporting these sheets is flat and sturdy. Use a solid desk or door panel and C-clamps or weights to hold the foam board securely against them. Other surface possibilities are ceiling tiles (Home Depot?), cork board, and thick balsa sheets. I think you get the idea. Good luck with your building projects!