Jimmy, it's relative humidity. The dew point at which moisture would precipitate out of the ambient, (saturated)air, dictates when moisture would form on your guns,(or floors) causing problems. The moisture on your floors is typically not coming from below. The tiles are below dew point, moisture is precipitating out of the ambient air. There are charts available to determine that dew point in regards to air temp/relative humidity. As long as you keep the ambient air temp above the dew point moisture will remain in the surrounding air keeping your guns corrosion free. I would consider 25% RH to be uncomfortably dry in my home and detrimental to wood. As was mentioned pianos and as I am aware guitars enjoy 50/60% RH. I am very sure gunstocks and furniture appreciate the same! I strive to keep my home around 50% RH/74DF year round. This may require adding moisture at times. Hope this helps.
Chief