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#21
You can mount the bay reservoir anywhere you want to. It doesn't have to be in the bays. I've seen them mounted on the floor of the case before.
EDIT: I've never seen it done, but it could still be mounted that direction. Just don't screw it down, it fits pretty good. Leave enough room in the tubing runs to slide it out to refill it. Just enough to get the fill port accessible. Besides, after getting all the air out of the loop, I've never had to refill mine.