I tried custom made waterslide decals on my fiberclassics Mustang recently. I also had to apply some decals over flush rivets. I brushed some softener (Micro-SOL) on the wet decal which sunk into every irregularity. Of course the dried decal must be clear coated. See the pic below. There is decal material over the row of flush rivets between the two text blocks and as you can see you see nothing, no bubbles or something else. From now on the waterslide decal method is my favorite method.