That vacuum method sounds very interesting. I've seen vacuum pumps used to evacuate air from air conditioning systems sell for $50.00 or less at auto parts swap meets, and that's what I paid for a brand new Robinair air conditioning service vacuum pump. I'd imagine you'd want your vessel containing the stock to be very well sealed so that the pump wasn't running continuously once you pulled a vacuum. Once you pulled the desired vacuum, you would valve it off.
I've often wondered if you couldn't do the exact opposite to get a finish to penetrate much deeper into the wood, much like pressure treated lumber. But pressure treated lumber is much heavier, so the added weight of a gun stock so treated might outweigh the benefits of being better sealed against moisture.
