In the summer time I rinse my horse off everyday later in the evening when it cools off a bit. Then once he dries I put on a coat sunscreen, then his fly spray then I put on his fly sheet. Everyday. It keeps him shiny, keeps his bay coat from bleaching out, and a cool rise off, to me, seams a great way to end a day.
I will give him a bath with soap once every two weeks, that just gets rid of the dirt that got under his fly sheet.
I have never had a problem with his skin getting dry. I do use Mane n Tail on his mane and tail, I know you can use it on the body but I use baby soap on his body, legs, and face. If I am going to a show, I will use Mane N Tail on his body and whiting shampoo on his socks.