Trying to set up a temporary power pole off a utility box for a 30 amp rv. Do i need a 30 amp box specifically or could i purchase a 100 amp with 4 circuits and just add a 30 amp to the circuit? Im not sure if adding a 30 amp plugin to the 100 amp box is possible? Id like to power the rv on 1 circuit and a water pump on another circuit. Any help would be greatly appreciated.