I'm guessing you are thinking of a second pull-out cord like the 30-AMP one you use now to plug into the camp ground 20AMP service pedestal. The hatch you show looks like the pull-out hole version hatch i use on my trailer.
If the second one is going to plug into the 20AMP Service Pedestal at the camp ground you might be better off getting a MALE receptacles on your trailer side to fit a 25-50 foot Standard Extension Cord fitting? On the inside i would install a stand alone 120VAC Receptacle in the area where this 120VAC 20AMP Service will be needed. Knowing me I would probably also install a separate 20AMP Circuit breaker inside the trailer as well for this separate circuit.
Running two pull-out cords from the same compartment will most likely get tangled up with the other cord coming from the same storage cabinet.
I do the same thing with my trailer using the 20AMP Service receptacle at the Cg pedestal. In my case I run the standard HD extension cord directly into the trailer.
I have used this 20AMP service for additional oil filled portable heaters and have on a few occasions brought along a 5K BTU Window Air Conditioner to sit in the second tent bed area to have A/C running from my 2KW Generator when are out on private property somewhere for a couple of weeks stay...