Just a thought that nobody's mentioned: Heated bay.
If you put the water heater in the same bay as the fresh/grey/black tanks, even tho it's insulated, there will be some heat given off that might just save you a broken water line if you're suddenly caught in a cold front. It does happen, even in FL. . .
Additionally, someone else mentioned this, but in the back bay is a lot closer to the head and kitchen sink than the old HVAC condenser compartment - thus less water waste potential, even with the recirculation feature.
If you stack your tanks, that will open up some additional space in the bay. Just make sure you've got sufficient support for the upper ones.
Not putting the water heater up front also allows you to use that compartment for your genset, or a couple of portable propane bottles (if you're planning on using propane for anything.)
Think nautical - sailors have been putting a quart in a pint pot for over 5,000 years. Our buses are simply land yachts!
FWIW & HTH. . .