I painted my truck in the garage with no plastic. Of course the garage was scrubbed clean numerous times before painting. I used furnace filters in the windows. Then I had a plywood panel same height as a furbace blower. The blower was put under the door and the gap filled with the plywood panel. Next everything was sealed. IF YOU DO NOT DO THIS you will end up with dirt in the paint. The door at the sides, at the plywood panel, and particularly at the top of the garage door was sealed with 6" masking paper. If not the overspray will blow back in the top of the door as a dry powder. The only thing I had get into the paint was a very small moth or miller that wanted to try and do the backstroke.
But that was taken care of and the paint turned out as good as any paintshop around here can do with a booth.