Here's one of the links suggested by bikeandan:
http://www.marxrv.com/12volt/12volt.htmIt's already been covered, but nearly everything operates on 12V using the battery or batteries in the trailer. You'll learn over time how much life you can get out of them depending on what you use and how much you use it. As mentioned, the furnace is the biggest 12V draw you've got.
When plugged into "shore power" a converter (converts 110V to 12V) recharges the battery. It's usually plugged into a regular residential-type outlet in the trailer. All the rest of your outlets will work when plugged in as well, and your air conditioning.
Fridges typically have a 110V and propane option but even on propane they need 12V to work. Some have a 12V option but I've found that not only does it draw a lot of power, it doesn't work nearly as well as the propane or 110 options.
