ORIGINAL: bhop73
To avoid decal silvering (what that 'sheen' is called), apply a gloss coat to the areas where you'll be putting the decals before you put them on.. or on the whole model if you want. Then flat coat it when everything's dry. The reason decals 'silver' is because air gets trapped in the rough surfaces of a matte finish.
DITTO!
Also, a decal softening agent for those uneven surfaces. Once all has dried, I use Testors DULL COTE over the decal and the rest of the tank.
HTH
~ Jeff