Using a home garage for painting a car is challenging. I want to do this discretely, so I don't want people to know.
I't looks like PVC piping and clear vinyl plastic duct taped up is the way to do it.
Cardboard door is an interesting idea.
I never thought about it, but ventilation needs to be done. I think the idea here is pretty good. Box fans in the front of the garage and exit fumes through the back.
Multiple 20' fans in the front (with filter behind them) and exit with 1 fan for exhaust.
The idea is having flammable fumes not be ignited. That is always the safety concern.
This will lead into lighting. LED lights need to be explosion proof.
plus having a light source on a mobile rack could be helpful.
Now to talk about the air compressor.
paint tent1!
http://makelyhome.com/50-diy-collapsible-spray-paint-tent/