Originally Posted by Zephod_beeblebrox2
One breaker feeds the left side of the sub panel. The other feeds the right side. The cable for each side is 30A.
Advantage... When I'm on a 30A circuit, both breakers in the mini box can be on. On a 15A circuit, I turn one off and just have two active sockets.
When you plug into 30 amp shore power your system up to the individual breakers will be protected by a 30 amp SP breaker as long as you use 10 gauge wire up to the box. When you plug into 15 amp SP you will be limited to 15 amps by the breaker at the SP panel. Thus, the weak spot in your system, your 15 amp rated extension cord, will be protected at the SP panel. No need for your second breaker box. Just be sure you run 10 gauge wire from the outside bus receptacle to the breaker box. As stated before, you don't need a main breaker in your bus breaker panel, just connect your incoming hot wire to one lug and jumper from it to the second.
Here's a 30A inlet receptacle similar to what you'll see on most newer RVs these days
30 Amp 125V Boat Power Inlet
Here's a good quality 30A power cord that will make a water tight seal to the Marinco receptacle
Marinco 30 Amp Shore Power Cordset
You can build your own cords but the price is almost what a manufactured cord will cost and you still have to find a good way to weather seal the connectors to the wire. These cords can be found used on eBay considerably cheaper than the new price.
Here's the correct way to wire 15A or 20A outlets
Wire An Outlet