My .02 here. Half baths? Not a fan. But for us, its almost a necessity and it sounds like it will be for smithlaw, too.
Having the separate black tank is a pain. But our old Cyclone actually had the hook-up for the drain pipe behind the axle while all the other tanks drained in front of the axle. That really sucked because you had to hook up the drain pipe twice. Watch your step! But our Vengeance has all the tanks drain out of the same pipe. That helps a ton.
My son's fiance' goes with us from time to time. She sleeps in the garage. Its sort of her bedroom when we're camping. So having the half bath back there makes perfect sense. But if it wasn't for that, I think FR could have used that space for a pantry or something and it would be far more useful.
smithlaw. With your daughters sleeping back there, it may be best getting a half bath. Just be 100% sure the golf cart will fit; especially if you have three-season doors on the back. Our half bath takes up a small portion of a corner of the garage but we still have over 10' of room for the golf cart.