"I made 30 half-width inner covers the traditional way with masonite"
just my humble opinion from my experience with masonite inner covers, these were problematic for me; warping, moisture, condensation, mold, mildew, sagging. they don't stand up as plywood does. i have taken my old covers of masonite and ditched them....well, ditch but hang onto. i only use them for transporting bees with a large hole cut out with screen stapled on in hot weather, or catching and moving swarms. i also think, again just my HO and experience, i seemed to have more moisture problems with masonite covers during winter months. i don't like them and i won't use them. that's just me and my experience with these.