Brian may be able to answer this question a little better, but here is what I remember from him telling me about DIV and it raining...
I think he uses a couple of shower caps to cover the control box. White's is actually pretty good at securing the control box. My old XLT had been drenched with mud and water and it didn't have a cover on it at all. You couldn't see any of the black on the control box due to the mud. I cleaned it up and opened up the box to see what kinda of damage had happened...
It was completely clean and dry inside. But, I would definitely NOT chance it and use something like shower caps or plastic wal-mart bags.
I'm sure Brian will chime in soon...