Theoretically it would be more energy efficient then the space heater. It takes less to get it to temp and then it holds temp. I personally wouldn’t like this still at an option. It’s a little bulky and dangerous in van.
Mr. Heater F232000 MH9BX Buddy 4,000-9,000-BTU Indoor-Safe Portable Propane Radiant Heater, Red-Black https://www.amazon.com/dp/B002G51BZU/ref=cm_sw_r_apan_glt_fabc_WBKDZRA2MDZCM6NWCXE0?_encoding=UTF8&psc=1