All great ideas.
Check this out. Based on some of your ideas, I think what I am going to do is put down some 1/4" thin Hardi-backer board over the plywood, screw it down, and then maybe have the backer board floor surface spray-coated with Line-X.
What do you all think about this option?
Sounds like it might be a little expensive, but the Hardi-backer is highly moisture resistent, plus it adds strength to the existing plywood floor. Then the Line-X resists the wear and tear, and spills of gasoline,oil, etc.