On a serious note, I'd also be weary of water leaking down into the rear bank and messing with the coil packs; I think I've read that its a somewhat common issue.
I never let water get on the rear bank when washing the car. Most times I use Optimum No-Rinse at least on the top of the car so rinsing soap off isn't an issue. If the sides are dirtier, than a wash mitt and soap get used. I have only been caught out in any kind of significant rain once in the four years I've had it. My Master Blaster takes care of any water that creeps into hard to reach places.