Randy,
Now that I have something tangible to look at, I am thinking about partially doing what you are recommending RE 5/8" thickness.
What I am thinking of is, to build a mitered frame of Maple for both the top and bottom of the 1/4" box.
	- Bottom: Cut a 1/2" rabbet on mitered pieces to not only hold the OSD of the box, but to additionally provide the support for an inside-the-box floating floor/bottom of same, in Maple.
	- Top:  Cut a ~5/8" dado’d miter frame in Maple so that the actual Granadillo piece will become a floating panel.
 1.  This will give me more thickness for the longer hinge and latch mounting screws.
 2.  This will also allow me to have the top overhang the sides a bit.  May have to shrink the top panel for a best fit.
What do you think?