If you think about it when you bake a loaf of bread for a long time it doesn't get more moist, it dries out. The same would be true for your drift wood. In my opion baking would evaporate whatever water you have in it already therefore making it lighter. Even if you wrapped it in foil and were able to completely seal the foil, (which you couldn't) it wouldn't help it to sink as there would be no water for it to absorb. I always boil mine in a large aluminum pot on an outdoors propane burner and it works like a charm by not only making it sink but also by removing tannins and sterilizing it. I understand that may not be an option for all, so in your case I would reccomend soaking it in the bath tub and repeatedly changing the water as it cools down or starts to darken up with tannins.