For best results the epoxy has to be able to soak through the material and into the wood. At the very least, it has to completely adhere to the material. Otherwise there is the risk of delamination as the wood flexes over time under the glass. The result would be a large translucent or opaque bubble with microcracks that let water under the glass.

Epoxy does not bond well to most smooth plastics. I've never tried it with decal plastic, but my feeling is that it's one of the ones epoxy won't bond with.

Rice paper and cloth are thin enough that you can easily fair the edges into invisibility. Just put on thin layers of epoxy, let them cure and sand. repeat until you can't see of feel the edges. It's a lot like fairing the edges of drywall tape, but prettier with a lot less dust.

If you really want to use the automotive decals, put them on top of the varnish/paint. That's how they're designed to be used on cars, no reason for them not to work the same on boats. Just don't put them where they'll be normally submerged.

Good luck,

Laszlo