The AMP rating on charge controller depends on the AMP/WATTS of the solar panel(s).
Most cases leave current wiring alone and when adding solar + charge controller your simply wiring from the panel to the controller and from the controller to the battery. (IE: Charge controller, solar battery charge controller)
Many controllers have a fairly useless "load" set of terminals. In some cases this is for when the battery is fully charged and you really really don't want to waste the extra energy captured by your panel(s). The extra power can be routed to the "load".
In other cases the "load" is intended to be your RV. However most RV's also have a AC/DC converter/charger which feeds 120VAC and 12VDC loads.