Weather strip around the door frame (felt works really well), and a "draft dodger" on the floor against the door. (A draft dodger is a long tubular piece of fabric filled with batting, dried peas/beans or whatever.) A friend picked one up at a garage sale for about $.25US for me & it works great. I had been using a rolled up beach towel until the arrival of the dodger!
I load my film in there no problem, now.