Question: Is this a massive plank or quarter-sawn strips glued together?
If it is a massive plank you should count on it warping.

It is two pieces (both 2" thick) glued together. I don't need it until next
spring. I can get it close, leave it for a few months, and then finish it.
Would that help?

This is probably the wrong answer but I actually mean this:
Use the oak for something else. Buy some light wood like Western Red
Cedar and shape a board. Add unidirectional carbon for bending
stiffness and strenght. Sheat in glass-epoxy and paint.

Oak is about 50% heavier than mahogany, but I actually want the weight, so
that is not a problem. Besides, it is free and the cedar would be about
$50.