Re: inverter
You can look on the units you will be powering and see what the wattage is. It will either give you watts, or amps. If it gives you amps, multiply by the voltage (120) to get watts. Add em up and this will tell you what wattage of inverter you need. It would probably be best to round up and/or add a safety factor in case you add something or replace something.
Once you know which inverter to get, you can find out the amperage requirements of the inverter. Find a 12 volt source (wire) which will handle that current (large enough guage wire), hook up to it (making sure the wire to the inverter is appropriately fuzed) and you should be good to go. Your best place to hook in is right at the fuze box, so you are not adding a large draw to an already existing wire which may then be overloaded. Do NOT use an ignition switched source, as you don't want to have to turn the vehicle on to watch TV, and it is frowned on to have a TV visible to the driver while the vehicle is running.