My answer to your last question might possibly surprise you as it flies in the face of everything this group has been taught . . .
I spray the model with Matte Clear (Tamiya TS-80) BEFORE applying the decals!
I spray it on very dry to give the decal a slightly rough “toothed” surface to adhere to. I then BRUSH ON some Future just in the area where the decal is to be applied and while the Future is still wet I apply the water soaked decal. As this starts to set I will apply another top coat of Future to completely entomb the decal.
(This also does wonders to build a tiny transition curve/ramp between the model surface and the edge of the decal film, usually making the edge disappear entirely.)
I allow this all to dry completely (overnight) and then go over the decal area with several more coats of Matte Clear to hide the shine of the Future.
I try to preach this technique far and wide on this site but usually I get responses like “no way”, “old fashioned” or “Solveset is better.”
So to those folks that scream NO, I just say “whatever is working for you keep doing it!”
BUT . . if you are having problems successfully applying your decals then you MIGHT just want to try it my way! *
*Not really even my way. This technique was taught to me by Monte Kelch of Cincinnati. He is now retired from modeling at age 83 but the man has way more “wood” hanging on his walls and more first place trophies than I will ever hope to have!
Honestly NOT trying to beat a dead horse here but simply trying to exhibit unassailable proof of the technique.