Adding a plug

Yes, ou can use an inverter plugged into the cigarette lighter in the Winegard panel. On shore power this does not drain the battery and it still works off grid. Or you can use the inverter on shore power cord with the converter off and fridge on gas trick so all your receptacles are live--if your converter is not on the receptacle circuit--in which case you can separate them.

You can also run a 120v extension cable with receptacles at one end of it into your storage compartment from an existing receptacle on that wall if any. Remove the receptacle, shove the extension cable through into the compartment, widen the hole as required for the wire and now also the receptacle, bring the wire around to plug into the receptacle, and shove the receptacle back in. You lose the bottom half of the duplex, but still have the top half.

Or you can cut the wires behind that receptacle and "tap in." Or you can go down under and back up as suggested above by others.

I found it more practical to get a 12 volt charger for our laptop. My RV has little to no accessable wire to add more AC outlets. Adding 12volt DC outlets was much easier.

Thanks all...might have to run it under the floor as said....

Many rigs like ours have solid walls/roof/floor - nothing is run through the inside of them.
Rather, the idea of dropping a line through the floor from the breaker box, running conduit on the underbelly, then back up through the floor to the desired inside cabinet is a good one. I've used that method in our house as well, though I didn't need the conduit in that case.

If you run conduit from breaker box to the new outlet, you can use individual wires. I'd run three 12 gauge THHN wires (black for hot, white for neutral, green for ground) commonly available at your local hardware store.

You might be better to tap into an existing plug, run the wire on the inside of the wall through a conduit, through a hole in the floor, under the camper, up another hole to your desired location, through another conduit and attach a plug on the inside of your desired location. Attempting to feed a line in the walls of an RV is impossible without removing the outer skin or inside paneling.

Go to your panel. Pick up power there. Drill through the floor and run under floor to your storage compartment and then up the wall. If you use SO cord (service outlet) it is rated to be exposed.

Start by looking at the AC Breaker Panel. Wiremold surface raceway is sometimes a good solution to tap into an existing receptacle. There are non metallic box adapters, boxes and raceway available at home improvement and hardware stores.

Use a non contact voltage detector and start sweeping the rig. Check inside for receptacle location. No sense in making this harder than it really is...

This can be a challenge. Look for your nearest plug. My wires are in cabinets up high and along the wall attached to cabinet framing. Sorry I can't be of specific help