HI @Kamping Kay Let's start over.. Definition of Terms: Inverter = Takes DC, makes AC Converter = Takes AC, Makes DC. Your camper has a Converter built in (The AC plug thingie). It takes 120 AC, and makes 12 Volts DC. You have stated you want to buy a Battery (12V DC Output), and a Inverter (12V DC input to 120Volt AC output), to connect to your converter (120Volt AC input, 12Volt output). What someone should have said to you, Your converter should have unused wires on the back of it, that allow you to connect a battery directly to it. The Inverter is unnecessary.