Does temperature fluctuation also cause problems? I have moved my building to the garage and depending on the time of the year it can be quite cold or quite warm. I would liked to have keeper the work in the house but the dust got to be too much.
Wood has a low thermal expansion coefficient - meaning the size does not change much with temperature. However, the temperature of the air affects the amount of water vapor in the air (relative humidity), which will, over time, change the moisture content of wood. As a result, you may see changes in the size of the wood if you leave it in the garage at different temperatures.
Cabinet makers have long know to store wood at the same moisture content as it will eventually be used. In most houses, that's about 6% - 8% moisture content. Since, it takes time for the moisture content of wood to change, the first thing to do is keep your wood supply in the house, not the garage. Second, if you can, keep the model in the house when you're not working on it.
There may be another trick - over-dry the planks before putting them on the hull. As the planks come back to equilibrium moisture content, they will swell slightly, closing up the seams, just as planks on a real ship swell when the hull is put in the water. There was a comment earlier that this may cause the planking to buckle, but I doubt it.
FYI, a version of this trick is used by chair-makers to securely hold the bent backs into the seat. The ends of the back are shaped slightly over-sized to the holes in the seat. The backs are then dried in a small oven, just heated by light bulbs, to perhaps 2% moisture content. With the slight shrinkage that occurs the ends now fit (snugly) into the holes, but when the moisture content comes back to 6%, the end is solidly locked in place.
So, if you're too impatient to wait for the planks to dry, make a small oven above a light bulb (or perhaps a heat lamp or a halogen). The drying time would be pretty fast for pieces as thin as planking and you may get the added benefit of over-dried planks.