Yeah the bathroom and shower could be shrunk down. So I think this could work, but I will have to go to site to make sure I'm okay for the shower drain.
If my drawing is accurate, I should be able to accommodate a 96"x30"x30" with about 24" behind the tank and about 3.5" on the the sides (the 8'4" measurement is between the posts)
Any thoughts about this layout if it works? I still am not sure about allowing for front access to top and bottom and what if any material to make any cabinetry out of. All I know is I want to use some material that is already in use in the house so the tank looks like it is suppose to be there.