I made this sign by gluing numbers made of birch bark to another piece of bark:
This is for outdoor use where it freezes hard. The numbers are about 1/8 of an inch thick, and water will collect in the recesses and freeze and thaw until the sign is destroyed.
I wanted to protect it from the elements by coating it with many layers of spar urethane, until the layers flow around the numbers until smooth, but after about 10 coats, it's not happening.
I know I could use epoxy resin, but that would give it a glass block finish that doesn't really go with this kind of rustic look.
How should I coat the sign to accomplish my goal?