Curious why slow film and very long exposures? Shooting during daylight and getting long exposures? What do you mean by long exposures - seconds, minutes, hours?
As an example, I shot this Fuji 100 color negative during the daytime at 4 seconds even though the meter suggested 1/15 - overexposed by 6 stops, knowing the film can handle the overexposure without requiring pull processing or much scan/post work because most all color film can handle a great deal of overexposure. I needed the long exposure for the water to "fill-in" since it wasn't flowing much that day. This makes this ISO100 fiilm essentially ISO1.5 . . .
When I say a great deal of overexposure, I mean I can overexpose Kodak Portra 400 +10 stops and still get usable results without compensating for it in film processing with only. As you can see below, I took that +10 overexposed frame and did minor levels and white balance.
At that time, I had just started using Kodak Ektar 100 and wasn't sure how much overexposure it could handle since it was supposed to be a more contrasty film so I didn't push it past +5. Since then I have found it can handle as much overexposure as Kodak Portra 400 and don't hesitate overexposing it as needed.