You going to section the batteries into separate compartment(s) from the A/C right?
Batteries (especially wet cells) give off hydrogen when they are charging and I would think that you would want to keep that away from your A/C, especially if planning to use the outside air vent feature. The little units still have that feature, right?
I suppose the modern units must be less of a concern for sparking/arcing with sealed motors and solid state circuits, but... ?
Also, if you haven't already, you may want to take a look at how others have done there A/C installs. Many have run into more problems than they expected when they partially enclosed their units. I think Planovet had good success with his thru the floor vented unit in the Little Swiss trailer.
I'm sure you have everything well thought out and under control... just saying.
