You could get a propane tank and screw on heater like this...

https://www.amazon.com/Sunrite-Mr-Heater-SRC15T-Single/dp/B0054WH2T6/ref=sr_1_7?keywords=propane+heaters+for+indoor+use&qid=1666297064&qu=eyJxc2MiOiI2LjUzIiwicXNhIjoiNS43MiIsInFzcCI6IjQuOTMifQ%3D%3D&sprefix=propane+heater%2Caps%2C147&sr=8-7

it may not be sexy but it will be hot.