Basement humidity

I'm looking for ways to improve my basement humidity problem. I live in a very wet climate, my basement often gets humid enough to promote mold. It's sort of partially finished. Open ceiling, probably not adequate insulation, sheetrock walls, vinyl floor straight onto the concrete. My goal isn't to have a finished comfortable living space, but to have storage/mechanical space that isn't dank and moldy. The sump pit currently has a plastic lid that's cut away quite a bit to fit around the drain pipes, would making a 2-piece lid that closes more of the sump off help? The sump pump doesn't run very often anymore, we used to have poor drainage but I fixed that a few years ago. The drain tiles are external to the foundation so the sump pit is the only exposed water source. There are two HVAC vents in the ceiling, but no return. We leave the door open to the ground floor. The air handler is down there so it would be straightforward to add a return, but I don't know if that's recommended. Right now the only return is on the second floor. I did toss a dehumidifer down there recently, but it does use quite a bit of energy so I'm looking for longer term improvements.