Do you have filtering on the gun, I used to have problems with moisture blistering paintwork until I fitted a silica gel filter on the gun. When I have finished spraying I pop the cartridge off, put it in the airing cupboard or a low oven to dry out and then seal it in a ziplock bag till it's required again.
Never had blistering since.
The above is similar to mine but mine are 'pancake' shaped with metal threads.
Where do you buy these or the one you've got. They sound like a useful investment.