J, I'm a woodworker and what I would do is to use machine screws. You could easily drill a through hole in the steel. Then drill corresponding holes in your wood deep enough to accept a threaded insert. Machine screws with washers from the inside then holds the wood to the steel. Invisible and easy to remove whenever necessary. I would suggest using 3/4" ply. All the materials including threaded inserts are available at Lowes/HD. If you plan on painting then get the ply from the homecenter. Otherwise, get some nice cherry or other hardwood veneer ply from a lumber supply center. Should be easy to find in your area. Too bad you're not closer, I'd love to help you out.