Make a plexi glass case with a wooden bottom and a 3 tier step "Shelf" out of wood, with dowel pegs spaced on each shelf. Make the lid also of Plexiglass and hinged so it can be raised for access . If you space the dowels , some 16 pegs on each surface, you should be able to get 48 trumpets or so in it without the box being too big or heavy to move . Make the lid hinged with the swing towards the viewing public, and a hasp could be fashioned on the back side for security purposes . Sounds like you are going to be well received at the show ! Have a great time !