Dom, first in will protect your decals, a flat finish looks also more realistic and gives a good foundation for the weathering, otherwise you may get problems the paint to stick on the painted surface. What technique for weathering you have in mind?
Gerd, I'm totally new to weathering. Currently I've never praticed that yet. I'm going to train in short while with an old french prototype HO freight car. So I've no real basis to start with. However, I purchased a few Tamiya weathering sticks, I'm gonna try with them first. Dom