Lots of time on the router to take out the unwanted wood and trap some air in there, as well as gets the weight down.
It makes a great piece of art
A 3mm veneer seals it all up
A couple of coats of marine epoxy to seal it all and toughen up the surface.If you have good joints you could save weight and use lanolin.
Even better if you have made this for a mate.
These shots are taken from jordan_slides