RE: Roundtuit
Most people use the 2 3/8" or 2 1/2" sq. stuff. The rectangular stuff is a bit bigger in the one dimension, and easier to find, but normally has ribs in it. Maybe check for some fenceposts for different sizes. Doorskins can be made up pretty quick and even after painting take less time than driving to the Home D'pot. The plane won't be pretty anyway.