Since the bow is going to spend most of it's life in storage even if you use it every day I don't see any point in drying it any drier than your storage spot will maintain. Try and fInd a spot in your house that averages as close to 50%RH as you can get and keep your bows there. Even if you have a good seal on the bow eventually it will equalise with your storage spot. The RH around here is a bit high, sounds much like yours. You could build a warm box, just warm enough to offset your local RH, but it would have to be big enough to hold all your bows.