I don't do anything for my tortoises if it rains, except to make sure they are all inside their houses if its a cold rain. Don't forget, it DOES rain occasionally in the "real world" where your tortoise comes from.
A warm spring or summer rain has the same effect on Eastern Hermann's torts and Ornate Box Turtles as Marvin Gay and Barry White songs have on human females...if ya get my drift.