I personally usethis one for a 4x4 tent and it heats it extremely fast. Gets below freezing where i live and this can keep my tent at a steady 75
Wenatchee area here. I have a mini split in mine but also use this for supplemental heat.
I would strongly advise not to use propane for heat. With such a small space you will use up your available oxygen very quickly. In simple terms, deadly.
ISILER Space Heater, 1500W Portable Indoor Heater, Ceramic Space Heater Adjustable Thermostat Tip-Over Overheat Protection, Hot Cool Fan Electric Heater for Home Office Garage with ETL Certified https://www.amazon.com/dp/B07GBN86VR/ref=cm_sw_r_cp_api_glc_fabc_ua3bGb32MGQ07
this keeps my 2 car insulated garage at 70+ degrees in cold weather