I don't know how old your basses are but I thought this might be something to think about. My experience is that it takes 2 or 3 years for a neck-through bass to really stabilize. Until that happens, your action will change with atmospheric conditions, but most noticably with the seasons. And you will want to adjust the truss rods maybe twice a year.
But after those first years it almost never needs to be adjusted, and will stay in tune for weeks.
