Man, you have been busy and it's coming along very nicely!
Considering how you mounted your city water connection, I take you're not worried about anyone putting anything in your tank or system. Most campers in Europe and Australia that I have seen pictures of are using a fill with a locking door on it, and it's getting to be the norm here in the USA also. It's ashame that it's even something to have to consider, but given what's going on this day and age, I guess it's just reality.
Originally, I was going to use the same thing you did, but after reading some stories about that situation I started looking for some type of locking system and not just the boxes with the plastic door either. One of the things I looked at was a billet aluminum fuel door that could possibly be mounted over the water fill, providing it doesn't protrude outside of the body. If it does, it could be mounted from the inside and recessed using a spacer. These also come in square and rectangle shapes.
The sink looks really good sitting there, and I assume you're going to use a shower rod & curtain that 'bows' into the cabin to give the person in the shower a little more elbow room, right? I sure wish mine had a tall compartment in that same spot, because it's the perfect location for the shower whether it's inside or out.
I'm also curious to see how well that
Eccotemp water heater works. Is it going to be vented out the back side somehow?
BTW, I haven't forgotten about the stretcher brackets we discussed. I found a scrap yard here with three ambulances in it, but the owner doesn't want to part them out. The guy I talked to told me to wait about three weeks and check back if they don't sell, so that's what I'm waiting on. They also have a bunch of other goodies that I want.