The usual advice is to apply gloss varnish before decals, and then gloss/matt/satin as required on top of that, although part of the point of using Decalfix (or similar products) is that they're supposed to allow use of decals on matt or rough surfaces without the problem of air bubbling underneath.

I did several coats of gloss varnish on the Hurricane in an effort to see if it dealt with the paint texture problem, but the answer was 'not really'.