Try using a new hollow core door, approx. 30 in. wide. Don't add legs to it, just lay it atop a table. If the table isn't straight, shim underneath the door as soon as possible to prevent the door from warping.

They are cheap, straight and pins go right into it. When buying one, make sure it is straight. If you are going to build a lot of models and one side gets too much glue or holes, just flip it over and use the other side.

Good luck,

Dr. Wine