I use Deft Clear high gloss lacquer. I spray several coats over the entire sheet of printed decals. This locks in color perfectly and you get about 2 times as much bonder for the same price.
It's kind of weird. When I did restorations years ago, I do not recall having to do the sealer to the decals. HOWEVER I was using a different printer that had a heated roller It might have been a laser printer but I just don't remember.
I tried to find permanent ink cartridges, but no luck there.
Dan