Thanks for all of the comments and ideas!
Kyle, we weren't planning on tying the two cooling systems together. I was just intrigued by the idea. We do plan on trying to get two toilets in there, but we will see how it works. Also, thanks for the size of the big tank. I don't think that we will do one huge tank, up on top (we don't want that tank to cause the use of a casket, so it will be secure...). That tank will just be for extra, if we need it (the main tank would be below). Yes that engine does get warm. You have a good point...
Newbee, thanks for the ideas. We will be using a RV type of toilet. That is an interesting concept about the water bed. I think that it will be vetoed pretty quickly though
WEC, I think that is what we will plan on doing, is putting our main tank down in the bay. In addition to that, we are talking about putting another tank up on top, under that bed. It would just be a small tank or maybe two. That way we can fit them in the space that we need, around the engine compartments. Then securing it won't be AS huge a deal, because we have a (or two) smaller tanks.
JohnEd, thanks for the thoughts. We sure have a lot to work through.
This is great guys. Thank you so much. This is really going to help our conversion.