yes I see no reason it can't be done. However, my understanding of NEC code indicates several things to consider.
1) since it is a dedicated appliance it needs either it's own breaker or combined with another load and a load shed device. That is when the heater is on all the other loads are off. AC would be a good circuit for the load shed combo.
2) NEC code limits the number of breakers on a 30A panel (5?). Notice that's how most 30A trailers are wired. So in theory you are violating NEC code by adding additional breakers. That said, it agrivates me to no end to have the charger combined with the other 120V circuits, so I violated code and added another breaker to put those two on seperate breakers.
If it was me I'd add another breaker for the fireplace and not mess with a load shed device.