Winter Storage - Question

I store my '03 Zed usually from Nov until April of each year. She's fully detailed, gassed, and tires overinflated, and a battery tender put on before I cover it for the Winter. About every 4-6 weeks throughout the Winter, I remove the battery tender and start the car, letting it run for 20 mins or so. I let it get up to temp, and run the heater, A/C etc to get everything moving. Without driving the car, do you think I'm doing any damage by idling for 20 mins or so? My concern is that without driving it, it's not getting warm enough to burn off an condensation in the oil etc. This method has worked for me for years, but I just got concerned after reading another article about letting the oil condensation evaporate. What say you festers?