To cut down on the number of machined components, the thought is to use a table structure that is known to have a relatively good straightness tolerance ie extruded Al, and skin it with a material that is known to have a uniform thickness tolerance to create a planer surface for the rails to fasten to. A steel structure would require machining for flatness or an epoxy pour. I do not have economical access to machine long parts.
Perhaps this isn’t the best approach, but it seams to be the best given the processes readily available to me.
That being said, I would prefer to build the table out of steel...