electric for a electric heater

Before you start drilling holes in your RV find out what the CG policy is first.

Every CG I have stayed at, if they saw a cord coming out of a window, etc in 'addition' to the RV power plug plugged into the shore station.....they made the camper disconnect it. I'd just check first.

How about mounting a generator inlet box in a compartment or somewhere easily accessible. Run the wire from the box, through a small hole to an dedicated interior outlet.
Then just plug the power cord from the pedestal into the inlet box.
It will be a simple but permanent setup.

No idea here outside of running an extension cord from the box and somehow into the camper.

But on a side note, why no trusting of the camper wiring? We run electric heaters all the time when we're at campgrounds in the winter. Saves on LP gas. Ours are almost always rated 1500 watts and it'll run the entire time we're there with no problems. Plus, we've done this with all four of our past campers.