Not 100% sure if I'm following but this is something I did for pedestal use.
30A plugs in like normal.
I added a heavy 15A extension cord to run a ceramic heater. It doesn't interfere with normal trailer 30A power circuits.
Each trailer has it's own design and that's were things need customization. On my Classic I ran the cord thru the same hatch opening as fresh water, cord is coiled there when not in use. Plugs into pedestal. Then behind the lav sink and into the drawer under the fridge. Cord terminates at a duplex box.
Completely unseen until needed.
2005 Dodge Ram 2500 5.9L 6 Speed
16" Michelins, Hi Spec Wheels, Max Brake, Dexter 4 Piston Disc Brakes, Carslile Actuator, Equal-I-Zer, Dill TPMS. Campfire cook. BMV-712