Is your electric water heater on? I am currently running my 50 amp trailer off a 30 amp cord, with 2 1500 watt heaters on thermostat's, and a third on low (500 watts). In theory all 3 are 3500 watts when running, and the 30 amp service is 3600. Add in another 50-100 watts for the battery charger, and I am maxed out. The reality is this never happens. I have been using the same 30 amp 50 foot cord to power the trailer in storage over the winter for years. If I am going to use it in storage (at the house) over summer, I drag out the 50 amp cord for the ac's.
I would run 2 portable heaters on low (with thermostats) to keep the interior above freezing. If you want it warm to occupy, propane is needed, unless you get more power to the trailer.
