Most rv maintenance manuals will have chapters on electrical
code and practise relating to trailers and motorhomes but likely won't have a schematic for your brand and model as originally wired.
While you're waiting out the storm, think about this. A trailer, when on the road, is an extension of the tow vehicle electrically as well as physically. The starter battery
in the tug supplies 12VDC to the running lights
and signals. The hookup thru the trailer plug for this role requires four conductors. This is the simplest DC "system" for any utility, equipment, boat, or stock trailer. If the trailer has electric brakes
, another conductor is required. There are a couple more roles for a starting battery (charging a second battery, motorized jacks) which only complicate the understanding while fattening the umbilical between tug and tow.
Most small camping trailers have at least one 12V battery on the tongue. A good way to understand the role of this battery is to give it a name to distinguish it from the battery in the tow vehicle. In a boat, you'd call it the "house" battery to distinguish it from the starter battery for the engine. A boat is both conveyance and domicile just as is a moho or trailer/tug lashup. So the "house" battery supplies current to the bare necessities of life when you're "at home" (lights, fans, water pumps).
Problem with 12VDC house battery is that it's a finite energy source when the recharging role of an alternator in a moving vehicle isn't available. So your battery will discharge and the lights will go out. This is a problem your motor yacht doesn't have as you can always run the diesel for a few minutes and trade petrochemical energy for juice in the house battery.
Both the boat and the trailer are going to stop sometime and both can go on "shore power" (120VAC) when "at the dock." "House" current can do several different jobs. If you have both AC and DC lights, motors and appliances, those that require AC (air conditioner a prime example) are suddenly available. In the case of your DC lights and motors, AC provides the charging current for your house battery. To play its double role AC "shore power" is fed into an electrical
distribution panel which incorporates breaker-protected AC circuits and fuse-protected DC circuits in addition to a converter--a device which uses AC current to produce (or more properly induce) DC current for the purpose of charging the battery.
The side-by-side electrical
systems in a trailer can also be thought of as storage-dependent and grid-dependent. Might not seem that you're in a precarious position of "dependency" when you're "on the grid," but as you know, natural disaster can change your views on that in a hurry. Having both is not a matter of redundancy but of simple and self-contained vs. complex and technologically interdependent alternatives.
The following won't help you wire the Bug but is food for thought. In the early years of electrification in the U.S. and well before AC transmission lines were available everywhere, many homes and farms had small generators and storage batteries which powered pump motors and lights. In some parts of the world, that's still the case. Electrically-speaking, camping trailers have one wheel in the past and one in the present and are also a special case of the house/vehicle hybrid.