Are you tripping the breaker in your RV or at the pedestal? If at the pedestal, I assume it's only a 30 amp hookup, and you can solve the problem as MM says and not run any other big loads at the same time.
If you're tripping a breaker inside the RV, then you will have to see what else is on the same circuit and make sure everything else is turned off. A 1500 watt heater will draw about 12.5 amps at 120 volts. If the voltage in the campground is lower, the amperage draw will be higher. Assuming your circuit in the RV is 15 amp (most are), it won't handle much more than the heater.
We have a 1500 watt heater I can't remember ever tripping a breaker inside the RV. We always use one of several plugs that don't have anything else on that same circuit. We have, however, tripped the breaker at the pedestal when we forgot about the heater and tried to run the microwave or dryer at the same time.
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