There are pictures of the wiring in the Amazon reviews. Your existing pvc/wire will enter the bottom of the box. Black goes to the breaker then it goes to the plug. White goes to the neutral lug and then to the plug. Green goes to the ground lug of the box then to the plug.
Right now your black wire is going to the plug. Your wire is going to the plug and your green ground is going to the plug and to the box itself. The only thing different in the new box is that the black wire will be going to the breaker then on to the plug.
Don’t count on all of the reviews as being accurate and some are dangerous. One guy suggested saving money on wire by not running a ground to the box and driving a ground rod for grounding. This is very dangerous advice.
Again, right now your wiring should be black from your existing breaker to your plug. White from your panels neutral lugs and ground from the ground lug bar. Your service panel where everything starts should be bonded which means that the neutral and ground are connected together. If you were to run any 240 volt “sub” panels off your main service they would NOT be bonded so they would run four wires. You are simply running a 120 volt circuit out to your rv, its not a sub panel. Its no different than any other wall plug in your house other than it’s heavier gauge and you are now going to be able to interrupt the black wire.
