In general an electric heater draws a max of 1800 watts that is a 15 amp draw. Many home circuits are breaker/fused to 15 amps.
15 amps is also half of the 30 amps most smaller TTs are designed for.
We run our electric heater at the medium setting which is 1200 watts and it keeps our 25 ft TT in the mid fifties at night. That is where we like it.
During the day the cooking, washing and other activities seem to keep our TT warm.
We almost never run the gas furnace but it can bring the TT into the 70s in ten minutes.
I like electric heaters because they are safe and they shut off if tipped over.