For the doorway cover I’d go with a tarp and use some stick-on Velcro strips so it can be hung up and taken down easily
The oven will probably have to be set to its maximum temperature, and a small fan to help circulate the hot air will probably help
You should only use the oven as the heat source if it’s electric, though. Letting that much burned gas into a small space is really bad for you and possibly some kinda fire hazard. There are portable electric sauna heaters as an alternative
Keep in mind that if you have pantry items (rice, crackers, etc.) in the same room as all that heat and humidity, they’ll spoil faster
For the doorway cover I’d go with a tarp and use some stick-on Velcro strips so it can be hung up and taken down easily
The oven will probably have to be set to its maximum temperature, and a small fan to help circulate the hot air will probably help
You should only use the oven as the heat source if it’s electric, though. Letting that much burned gas into a small space is really bad for you and possibly some kinda fire hazard. There are portable electric sauna heaters as an alternative
Keep in mind that if you have pantry items (rice, crackers, etc.) in the same room as all that heat and humidity, they’ll spoil faster
Otherwise, sounds like a fun project!