A work of art Arthur. You have achieved amazing results on an AFV with figure paiting techniques (which are way more complicated that the ones commonly used when doing AFV).
You had problems with your decals because you applied them on a matt surface. The roughness of the surface traps air and causes silvering (shiny look). If you are ever interested in using decals, here is what I do (dont get me wrong if you already know this ...):
1) Gloss coat surface. Future(US) or Klear(UK) floor varnishes are recommended
2) Microset applied to the surface where the decal is going to be applied
3) Apply decal
4) Let dry for a while
5) Apply Microsol, which will wrinkle the surface of the decal. But don't panic, and let it do its work
6) Let dry and dull coat it.
This process will give the decal a painted-on look. This process is vital if you want to build a plane, but yet not that vital in the case of armor.
Hope it helps.
Zverko