TV and lights are OK, the space heater is a no-no. You can cook the extension cord and running the heater with anything else can possibly damage things. Most space heaters are 1500 watts (12 amps). Remember, you have a converter and battery charger (and assorted other control circuits) quietly running in the background all the time adding to the current load. A 15 amp supply is only safe for keeping the batteries up when the RV is in the driveway. Offer to buy the relative a 30 amp power post that they can use once you are gone....
