My only concern with using the electric heater and AirCon together is the amperage draw if both kick on at the same time. That can easily exceed your 30amp system.
I had to be too cold with the Air to keep the humidity down and not sweat in bed in my Wolf Pup last year. If possible temperature wise, a cracked window and a vent fan on works better. I did buy and use one off those electronic dehumidifiers. It helped some, not near as effective as a compressor type, but uses much less power. A compressor type D/H uses power similar to an AC unit. It will eat up most of your available power.