Take a look at the maintenance manual diagrams from 1975 here:
These are on the edge of readability, but I can post a better file if you need it.
Regarding your diagram:
1. Per the diagrams in the post above, you don't need a lot of separate 12 VDC circuits, maybe 5-6.
2. Be careful about how you wire the 110 V inverter. I would not connect it in parallel with the shore 110V, which means you need separate sockets for its output. You also need to provide a switch for turning it on--you can't leave it connected to 12V--even without a load it draws some power and you'd soon find yourself with a dead battery.
3. In general, I think it is a bad idea to use an inverter in an Airstream. Maybe it's OK to power a shaver or charge up a cell phone, or maybe even run a laptop for 30 minutes, but you need to consider how many Watt-hours you have in your batteries. For example, a 75W laptop would draw about 9 amps through the inverter, considering conversion efficiencies. I see you have two 6 V batteries, so I'm thinking you have about 200 amp-hours at full charge. You never want to discharge your batteries below 20% charge, so you've got 160 am-hours available. One hour of laptop draw is 6% of your total. How many days will you be out? You've got to also figure all your lighting, which takes most of your amp-hours, believe it or not, even with pumps and fans (the ceiling fan will be on a lot, and during the day, so this is a major power user) and whatnot. If you're thinking you need 110V for 4-5 hours each day, you need to think about a quiet generator if you're out for 5 days or more. I'd be interested in what you find once you're actually camping.
4. I see a gray to black pump. What a great idea--gets rid of a second thetford valve. Can you give me more details on your plan? I've seen one other Airstream where gray water is used to flush the toilet, which would require a second pressure-switched pump, also not a bad idea.
5. IMHO, I don't think you want to drive the heating elements in the WH and Fridge with 12V
. If those circuits are just for auto-igniters, fine. I and many others drive with the fridge operating on propane. I know there are 3-voltage fridges, but you can only use the fridge on 12V
while the tow vehicle is on--you'll find the propane saved just while towing is minor and not worth the dead battery you'll give yourself when you forget to change the fridge to propane.
6. The Blue Sea is expensive, I think recall seeing. You can do fine using a small fuze block for automotive fuzes ($15 or so). You only need 12V
circuit breakers in two places--the tongue jack and the tow vehicle power line (longer explanation available, if needed). The rest of the circuits can rely on fuzes of the blown type. These fuzes are there to prevent fire and damage due to a failure in the circuit, which rarely happens. Emphasize "rarely." I mean like never. They usually blow when you're fiddling around with the wiring or installing something new, so in normal operation you won't ever (a slight exageration, of course) need to get at them. I use an 8-circuit fuze block--two 40 amps for the batteries (which provide for a nifty battery switch at not cost--just remove the fuze), a couple of 20 amp and 15 amp circuits, and a low current 5 amp circuit for the battery monitor.