We do this all the time at the campground pedestal using this 20AMP Service which does not take away from the other 30AMP SERVICE connection.
I never wired up an outside connection on the trailer but just ran an proper sized extension cord into the trailer. The basement door might be is a good spot which has a weather seal strip around the door edge. You can pass the extension cord into the trailer here and fish it up inside the trailer through the dirty laundry door located in floor of the bedroom wash-up cabinet.
We carry two of the 1500WATT OIL-FILLED Electric Heaters just for this reason...
For us the OIL-FILLED heaters with no visible flames or open red hot cores are the safest to use unattended in the trailer.
My trailer which is used most often used is a OFF-ROAD POPUP unit which has the velcro window flaps etc and running the extension cord into this trailer is not an issue.
I also use the 20AMP SERVICE connections at the camp grounds pedestals for all of my outdoor 120VAC connections for lights-fans-etc... Sometimes you have to guard this connection pretty good as other campers especially the close-by TENT CAMP SETUPS will run an extension cord to your pedestal for their use... ALot of places we go to has both Electric sites and NON-Electric sites in the same vicinity of each other. Westmoreland State park in VA is setup this way... Kinda easy to figure out who is doing it - just unplug it and listen for the loud yelling haha... Of course I have no problem with sharing if I have been asked.
I got caught one time plugging into 120VAC on an outside wash-up sink area at the rest room bldg at Loft Mtn VA on one tent camping trip. There stands a Ranger waving his finger at me holding my extension cord trekking across the woods going straight to my tent site haha... He said cover it up with leaves better next time. So when he left I ran it again and covered it up better with leaves hehe...
Every tent setup should have a TV SETUP to watch.
Roy Ken