How would you put these together?

[Sam Puhalovich]

Cut-trim-fit the pieces to the shape that you want.
Bore-cut recesses at the 'touching' spots at the bottom for connector bolts.
Cut a piece of 1/2" ply to the shape ... staying 1.5" inside the shape.
Install the connector bolts.
Screw the plywood to the bottom side.
For that matter ... you could eliminate the connector bolts.

[Jim Matthews]

Tic-tac-toe frame with a plywood skin on the bottom would make an excellent torsion box.

I wouldn't do to much fitting of the top pieces, side to side - you'll lose to much material
that can't be patched. This sort of thing calls for a stout marine epoxy and some kind of splines to align pieces laterally.

I'm thinking chainsaw mortiser, or the equivalent.

[curtis rosche]

Heres the top put together. Off to panel sand it tonight

[Frederick Skelly]

Thanks for the follow-up Curtis. I wondered what you decided to do.
Fred