I have an old Brower 845 metal incubator. I'm able to keep the temp between 101-102 as the manual states, but I'm unable to get the humidity up to 50%. It's staying right around 35%. I have a sponge in the water dish. The unit has vent holes on top...should I plug a couple of those up? and if so, what can I use for plugs? I don't have eggs in the unit yet...I have hatching eggs arriving tomorrow. Help!