John,

I'm no expert, but can relate my experience using loose tenons on a
large rolling wood rack. It was made of milled 2x4 and 2x6 rails with
28 loose tenon joints. I did the traditional approach of making them
close to right, then used a hand plane to fine tune the thickness of
each tenon so that each had an ever-so-slight drag in a piston fit that
could be moved with hand pressure. After applying glue, I had to
assemble quickly because the wood swelled and "locked" in place. My
impression was that I had some tolerance in fit because the swelling
wood "self adjusted" to a tight fit. the precise thickness, no swell
character of the fiber board may work against you because it requires
such a precise fit to be effective in the joint - too tight and there's
no room for glue - too loose and the glue won't fill the gap.

Bob