You need to read the topic RV Electrical Safety
and all the little articles linked to within the thread. Mike Sokol has been kind enough to keep up with the thread and keeps posting more info. BE SAFE!!!!
The easiest way is to run your interior wiring to a small panel box. Plug into the power pole OR plug into the generator. No switches.
Ours is a Square D brand Load Center QO6-12l100S with 6 useable spaces (2 are voided for wiring unlike the one shown and linked to) filled with 6 double space 20 amp breakers. Could have used the super skinny breakers and put two in each slot but that would have been very pricey and wasn't needed. Our panel box has been discontinued but looks like the one above. We had thought about using Progressive Dynamics all in one panel box (combines 12VDC and 110AC in a single box) but we wanted/needed more circuits that the PD allowed. The Progressive Dynamics Smart Charger w/ Charge wizard is powered by a dedicated 20 amp breaker in the box. The cable runs from the power load box to the 30 amp receptacle power pole in the campground OR it can be plugged into the 30 amp receptacle on a generator. We do not have our generator yet. But we will wire a receptacle in the electrical bay that will be fed by the generator. The Bus will the plug into that for generator power. It's an "either/or" idiot moment proof set up. This way allows us to not a have a stupid moment and plug the bus into shore power WHILE being plugged in the the generator (or vice versa). That would cause a lot of damage.
Get a panel box that uses breakers that you can buy anywhere (and carry a couple extra with you). I had a friend in CA who had to order his breakers for his vintage RV online. Whereas I had the same GE panel box in an RV manufactured by a totally different manufacturer within the same decade. I bought my breakers locally, not online. I don't think it's as big a deal as it used to be since I know that I can buy many of the same breakers here in the Southwest that I could in the Southeast (GE, Square D, Siemans). But it's something to keep in mind. Always test your breakers, they should not be "silent" when they trip/reset. A silent breaker may be a bad breaker. Yes you can buy a shiny unused bad breaker straight from the factory.
We have only three 12vDC items and that is the water pump (Shurflo 2088 Classic) and the 12vDC fans on the rear heat exchanger plus the hot fluid pump also on the rear heat exchanger. A dedicated inverter (currently only the one) powers the 110vAC LP Gas range lights/electronics, 110vAC thru-the-wall-mobile-home exhaust fan over the range (our version of a better working hood vent) and all the 110vAC fluorescent lights. The smart charger charges our "house" battery bank (currently our one and only cranking battery) while on shore power or while on generator (when we get one). Once we are ready to buy a house bank, it will be two to four 12vDC deep cycle marine batteries. It will be set up to crank the bus via a switch or run all four batteries as a house bank with the smart charger keeping them up as needed. I might put the TV on a dedicated inverter. Not sure. We have wired to where we can easily make the change. We like to watch a movie when Freedom Parking
. And we could do that with the battery bank we have planned without running the generator.
This set up took a bit of thought on our part. Our setup is not like others on here. We are working fulltimers (I have a job at Home Depot). Our bus is our Residential Vehicle, not Recreational, and is set up as such. I have a 30" LP gas range, 8.8 cf AC refrigerators, 12 cf AC upright freezer, 10 gallon AC water heater on board... the 24" wide standard dishwasher, top loading washer and LP gas dryer have not been bought and installed yet but they have been planned for and space allotted to them. This is our only home, not a weekend play toy. It does not move until we are ready to leave. We have been in our current location since December 2011. We will move to Texas in September 2015 where I will get another job plus start another shoestring business of our own (I don't like working for others). We need to be self contained on our moves since we tend to stay in parking lots when we travel, only pulling into a campground every 3 to 4 nights to dump and refill tanks (my fresh auto fills). This is how we live and travel. Not everyone does. It's a large part of the reason we converted a skoolie. Before you run the first wire, build the first wall or cabinet, you need to figure out HOW you will use your bus both now and in future years. This will save you a great deal of headaches if you have a good plan and are armed with knowledge (or speculation)