The Spruce Goose was actually make of birch, with much of the adhesives developed at the time, by the Hughes organisation directly.
Very strong stuff.
About the tail.
Hughes mentioned to Donald Douglas (Sr) later on after the one and only flight, that the tail vibrated terribly on liftoff, with a violent twisting motion.
I know this only because, my Dad was a Douglas executive (engineering project manager DC-6 and DC-7) and knew DD quite well.