Jeff.....the ground-work or (track) of any sliding door that you expect to hold-up under the weight of a 50-90 lb. sliding panel, with metal rollers, for any period of time HAS to be made of aluminum. The thermal conduction of any metal is going to allow cold to transfer through the ground-work to the moist, humid air of the interior. Is there a heater duct just in front of the doorway? Do you have full length drapes or blinds that trap warm moist air between them and the door? You might try to lower the humidity of the home. A thermal-break or barrier is any interruption of cold transfer in metal surfaces. Why did you remove the Marvin doors? This is a common aggrevation with alumimum windows and doors. That is why vinyl window companies flourish, but longevity, and durability are on the side of aluminum...put a towel down there and keep the humidity off the ground-work.........BG