Well not really irrelevant; info discovered here might help others even if I'm upgrading. But something I should mention is that there is a sliding metal door on the back of the hood that is meant to stop air drafts or large amounts of water and dust. Of course it isn't sealed and water or minor dust might get through. I suppose one could use sealant (caulking or weather stripping of some sort) to seal the three pieces together pretty good, isolating the internal wall segments. So if it was me and I wasn't doing a full rebuild and just wanted to attack this one area, I'd at least make sure the channel through the wall was sealed well to prevent structural water damage.
