I built a floor-to-ceiling bookcase about three years ago, and used painter's caulk along the joint between the bookcase's top edge and the ceiling. Every winter about this time, a hairline crack opens up iin the caulk. I'm sure the very low humidity in my house is very much to blame. But now I need to recaulk this area. Last year I tried bathroom caulk because I thought it might be more flexible and resilient, but that didn't solve the problem. Is there a better type of caulk that would be more resistant to cracking?