I have not tried painting in 40 degree weather myself. But having seen the results of a professional shop that tried it several years ago with bc/cc, I invested in a heat pump for my shop. Bad sags and runs. Owner said that after he sprayed it, it looked great. Came back the next morning to a real mess that had to be sanded off and reshot. I would say try a test panel first on something other than your vehicle.
