More progress, some answers, and more questions...
We launch on a week-long work and play trip to Moab on Monday of this week. Ironing out the little things and getting others "good enough".
I ordered this water pump from Amazon. Figured that it was worth a try for $12. Seems to do the job. Simple little thing. The faucet on/off doesn't seem to work. When the pump is running, water comes out of the faucet whether the knob is forward or back. Which is better than the alternative. We'll just turn the faucet on and off with the water pump switch.
The $12 pump came with two unlabeled wires sticking out of it. I just guessed. Couldn't tell you now which colors they are and which I hooked to which. Similarly, the water fittings aren't labeled. Is that just what I get for $12? Or are both omissions related? Like, if I hooked it up to electric one way would water go left to right and then reverse the wiring (polarity?) and it goes right to left? Doesn't matter, as I seem to have gotten lucky.
I've got an outlet wired into the fuse box. One dual usb plug and one 12v socket. Seems to work. Just have to mount it into the plywood cabinet.
I know Vic Harder's answer to this next question ("get the Trimetric 2013 Monitor"), but I'm curious as to what my other options are. Mainly, what are my cheaper options? Now, hopefully my ignorance is clear... I don't know jack. Am I right in deducing that voltage out of the battery, under some sort of load, can serve as a proxy for state of charge? Like, I can watch the voltage and use the attached chart (or do I need a chart specific to my battery? Specific to the type of battery? Size of battery? Specific to the phase of the moon?) to keep from totally screwing up my battery?
Lastly, for now, tell me about safety sensors. There's propane sensors, smoke detectors, CO detectors, and something really cool I don't even know about. What do I need to keep from waking up dead? I ain't afraid to live on the edge a little bit. I'm sick of dumping money in this thing, for now. And I'm also sick of giving up space...
Speaking of, anyone mount a roof rack on their truck cab in front of the cabover? Any clever ways of cantilevering a rack out a little? Like a storage visor?