I'm debating between the dometic 13.5k btu or the 15k btu. Walls are finished and has rubber coin flooring. On first thought, I was going to go with the bigger unit. Using the logic bigger is better. But then I read somewhere that if I go too big, then the air will not be dried as it cools, may stay damp in other words. Any thoughts on which one will work based on the size trailer I have?