One last thing, I leave my home's furnace fan on 24/7. I figure that has to help keep the air moving throughout the house, and since the dog is in and out all day, I get plenty of fresh air introduced during the course of the day.
TIf I understand you correctly, sealing those combined with the open exterior sump pit may allow for enough venting.
I was going to wait until siding is finished, but maybe I'll get the meter and check things now. If I don't have to do the Radon vent I wont' have to block out a wall penetration for it and that would be nice.
I believe Ryan Lindberg has a radon mitigation business. I’m not sure if he’s a member on here but I know someone here will have his number. He’s someone I would very much trust setting a system up