PapaB,
I plane both sides of two 2X4 4' long, then I shim them to the proper taper. After you get them shimmed, screw them together and countersink the screws so they don't hit your planer blades. you can use printer paper for shims, the paper I used was .003. Make your .002 first, then make another .002 and screw them together to make your .004.
James.................