Try digging a small trench outside the coop to divert run off away from wall.I think it comes in underneath the walls. When it rains, there's usually runoff that runs down beside the coop in a crack, and I think it seeps.in. I've tried putting more dirt up against the wall on the inside, but it hasn't helped much.
Best done when it's raining hard so you can see where the water is going,
not fun but very effective.
When you say 'crack'...does that mean a crack in some concrete or.....?