I had thought to go the porch paint/sealer route, but I made the mistake of asking someone at the store about that and they looked at me like I was crazy, as though that could never work.  I listened and went with thick plastic stapled to the floor instead.  I regret doing that.  The chickens scratched a lot of it up, and what was left made it REALLY hard to clean out the coop this spring.  My shovels and rakes just got caught in the remaining plastic and it was all a big pain in the butt.  If I had it to do over, I would either paint or put down vinyl.  However, I will say that my plywood coop floor was not at all wet under the bedding, and I think that keeping the water outside the coop helps tremendously with that.  They don't drink in the dark, and can get their lazy butts outside to drink during daylight, so I've just kept the water and food outside.