Cheap heat. Run out to Walmart & get a couple of ceramic heaters. The trick is not to overload a circuit. Check to see if all outlets are on one circuit. Split the load or run one heater on low power, the other on high. Between the heater specs & circuit breaker rating not hard to firgure out what can & cannot be run together.
More than likely the built in electric heaters are on their own circuit breaker.
In Newfoundland earlier this year we had nights in the 30s & got by without using built in electric heaters or propane furnace. The little portables, one on low, one on high, did the job.
