Maybe this diagram will help. It was prepared by a guy who goes by Merlin on the Aluminumcamperforum and is for a 100 watt system. I hope he won't mind me posting it.
To make this into a 4-100 watt Renogy panel based system, you will need to wire the panels in parallel and use bigger wire, at least #8 gauge wire and maybe even #6 for minimal voltage drop to wire from the parallel panel junction down to the controller. The controller will also have to be bigger- 30 amps and be an MPPT type. Wire from the controller to the batteries with #6 or 8 gauge wire as well. The Bussman 20A breaker will need to be upgraded to 30 amps also.
If you are going to use conventional lead acid batteries then that is all you have to do. If you are going to make the tongue mounted batteries into a Li system then there is much more to do and I am not about to touch that.
David