Best way to keep condensation out is to make sure the engine gets up to temp. Its a rare occasion that I start up one of my vehicles and not let it warm up to temperature even if its just to back one out of the shop...I let it run till temp gets up. Condensation will also rust out your exhaust system.
Personally I see no reason you can't use a vent cap plug the slots. That's what GM did anyway on a lot of engines. Just as long as it can BREATHE. ...others may feel differently.
Even in Tennessee it should reach temperature. Perhaps your gauge is wrong. Check the temp by putting a thermometer in the radiator neck, or if you have an infra red light check the top of the tank where the return water is coming back in. If you have to put a piece of cardboard in front of the radiator for a while to see if that will help it get up to temp.
