Garage walls

[Garhan01]

I have a concrete sectional garage,wich I have insulated the walls with,
fibre wool insulation,then a vapour barrier,then finally 18mm exterior ply.
I now want to paint the wall,and was wondering if,I should seal the ply first,if so what with?I am a little concerned about damp,as a lot of water
must come in during the winter,when the car is getting put in wet most of the time.