A space heater will draw 1500W and will kill your batteries just as they would with an AC unit off your inverter. There are other fossil fuel based heaters which are better suited for vans. Save your space heater for shore power.I think I can keep my AC needs to when I can run a generator or connect to shore power.
I do think, however, that my wife will want to run a small space heater if it gets cold.
Revising my electrical needs, I’d probably include these on my list:
Charging laptop/phone etc
Could the system you suggested handle that?