OK, don't laugh. But I put the open box in the bathroom for a few days and make sure to steam up the room really well during showers. It would probably be even better if you had a humidifier and stuck the open box in a small room for a few days. The wood will only pick up a little moisture and then re-equilibrate when it's back in 'normal' room conditions. But for old kits, I really think it helps a bit. Oh, let the plans sit in the room with the kit, open to the moist air. They shrink too after 30 years!