I installed 3 permanent recessed electric heaters totaling 2,000 watts. I used a current sensing relay for demand control so that when the main 30 amp supply current gets above a preset adjustable level, the heaters are automatically disconnected. We can run coffee maker, toaster, MW and other loads and never trip a 30 amp breaker.
The limitation on breaker spaces in RVs doesn't exactly make sense. I installed a recessed vacuum unit and needed a dedicated 15 amp breaker and for the heaters, a 20 amp breaker. The only way around it is using tandem breakers which I have zero issue with doing.
For a dedicated heater of any kind, I'd install a separate dedicated receptacle for it wired directly back to the panel.