My way is not to code, but it works fine for me.
I used grey colored standard ones that I bought at Home Depot. I mounted them sideways & labeled them "12V" so I don't confuse them with the standard 110V ones that my inverter powers.

Also, I used 14 gauge romex vs. the standard 16 gauge on all my wiring. My 12V loads are light, so I did not need 10 gauge romex. Depending on what your loads are you might need the 10 or larger.

So just keep in mind the loads and add the larger wire where you might need it, or multiple runs.  I had planned to use much more 12v when we built, but we use less then I had initially thought, but I am still glad we have some.  It is also nice to know it will work even without an inverter.

   I've looked at raceways for some time now and to wire a house for low voltage requires a complete load calculation. Breakers at each connection point (device)and at a distribution panel. With a UL approach to overload protection .The one thing that will put anyone out of power faster is a short  This is real when a bunch of devices are on a runaway supply of 200 or 400 amps . Burning the house down is not an option.

 Yes there are 12 volt codes, I've seen the code book. A lot of it has to doo with wire size and safties but the point is there is code. We are doing what your talking about (living on 12 volt) and I've noticed that most things that run on 12volt are more efficent in terms of energy consumption. On the wire size ,what we did was to put the 12volt sevice pannel in the center of the house to minimize the lenth of wire to the rooms. then run heavy cables to the panel. Don't cheap out on wire size, do it once and do it right (heavy wiring) and it's not a problem.

 The insurance companies are a pain when it comes to insuring somthing they don't understand but shop around you will find what you need

 We are presently building a cogeneration setup for winter heat and power and have just drilled our well (100'). Our well pump (submersible) is 12 volt and moves 4 gal a min at 100 watts.

 My point is it can be done on 12v and done well.
 good luck in your endeavors and don't let people get you down

 12 volt rules

We ran 12v with 8 ga THHN (bought the red 250' roll cheaper than 2 100' rolls of 10ga, permanent markered the negative black. I'm the only one messing with it.)the whole way.

We striped 1/2" where needed, and dropped in 14 ga 2 conducter "trailer light plugs", from the top through 1/4" holes, then soldered them in to the 8 ga.

Easy and cheap to add or remove a plug. The 1/4" hole in the floor behind the carpet tack strip, under the carpet, will never be noticed.

Have an adapter, trailer plug to lighter socket, for things that use it.

8ga reduces the V drop. 16" of 14 ga won't count for much. There is no danger of plugging something into the wrong voltage or backwards.

This is a smaller system, 1 battery, 1 panel. Most loads are 1 amp to 4 amps, and not many at once.