As a high days and holidays car for enjoyment rather than practicality, I purchased a 2002 MG TF from a respected MG dealer. While waiting to clear out the garage, I've kept the car on driveway for past five months with a semi-permeable protective cover. All well and good when we experienced a relatively mild winter, albeit rainy and windy but no snow.

After some harsh frost this past month and I've noticed the interior of car is damp, I've checked usual culprits and the car is free from debris and leaves. Cranking windows open an inch, under protective cover is my first strategy. Have you any advice or opinion as to possible causes of this muggy dampness?