Protective Decal

Protective covering over decal and painted surface-Corn hold games?
I have built two different corn hole games. One I have painted with red and blue oil based paint. The other has scarlet and grey latex paint. I have decals I want to install on the games. What protective product should I use to clear coat the game board (including decals)? Should apply a coat or two of the protecitve product before I apply the decals, and then apply a coat or two (or three) of the proticeive product over the decal?
Several coats of Varnish,put on after each coat has dried should help.
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