http://jkcallin.blogspot.com/ "As I wandered, alone, through the endless fields of corn, I could hear the crows. They seemed to mock me, calling out my name, over and over", said Cawe
It would be more of a challenge to seal on a side wall than at the rear where I think the trailing draft and roof overhang would help keep moisture from driving in.
I don't see a good reason for it, but then some people might say that about camping in a little box.