If you're positive breaker, reset, fuses are all OK, only thing left is the element. You should still be able to run it on propane.
If you are familiar with a multimeter, here are a couple tests to do on the heating element.
Measure voltage across terminals on heat element when it SHOULD be operating. Voltage should be same as what you read from any of the wall outlets in the RV.
Turn off the power to the heater (turn off breaker or disconnect shore power), disconnect the two (or three) wires of the element, and measure resistance between terminals. Around 10 to 15 ohms (if I'm not mistaken) indicates element is good. No resistance, element is bad.
Measure resistance from each terminal to "Ground" (Green screw or bare wire). It should be "open circuit" (Same as test leads not touching anything).
