Keeping bike kit in garage.

[fazersharp]

What causes it is the sudden change of temperature if its been a warmer winter day and then suddenly get cold and that causes condensation, like the early summer months when the evening coms and everything can get damp, especially cold surfaces. The asbestos roof is very thin and the cold travels through to the warmer underside causing the wet, I would add a layer of insulation 2 or 3 inches under the roof leaving breathing space between the insulation and the roof, 25mm kingspan would do the job with minimal support needed.
I wouldnt disturb touch or paint the asbestos - leave it be.