Oh dear!
Is it condensation or is the water coming in from the outside? Either way, pain in the bum.
I get this inside the trailer where I store stuff. I muck about covering everything with tarps.
One good thing about the garage, I don't get this problem probably because it does have a bit of heating but also it has drafty old fashioned up and over doors. But it runs off the roof in the loft
.one of the problems of having it well insulated.
Each fecking thing you do to try and improve the house and make it more economical to run, seems to lead to other problems.
We all suffer with condensation in the loft on our estate. The timber frame construction is so good you only have to add a bit of loft insulation etc. Various people have tried various things, the opposite neighbours had little chimney type things fitted, they were a disaster resulting in the ceiling falling down in their living room!
Most add extra air-bricks in the end of the gable, I am hoping the new soffits will breathe a bit better, so we are hanging on!!
Do hope you get it sorted!