Have constructed 4 stackable trays to hold wrist watches. Sides of tray are 3/8 walnut with 45 degree miters on ends x 2" tall & bottom is 1/4 oak plywood. Am trying to hold assembly together & square to glue. Will be cross cutting miter to install contrasting key when glue is dry. Using Ash or Maple for key. What is best way to hold pieces together for glue up ??