A couple things come to mind that may help you out here.
One is to put a clear gloss coat over the flat paint apply the decals. Then after they are dry put a coat of clear flat over the paint.
Another idea I have heard of but have not tried is. If you don't have access to microsol products is to try a water/ vinager mix. Something like 1 part vinager to 5 parts water.You may want to try this on a scrap model and decals before appling it to the plane.
Hope this helps
Paul