Howard Acheson or Rob (McRabbet) are a couple of the experts in this arena. However, a question:
What is the brand and labeled name of your "Tung oil"?. Many products labeled as such have no tung oil in them, and are either oil/varnish blends or just wiping varnishes.
The BLO will add amber hue, but will be slow drying. Depending on the ingredients in the tung oil, it may darken over time, or give that same amber hue to start with.
If you have some scrap from the building process, I would try some test pieces first.
The clearest finish will be a water-based (acrylic) "varnish", but the use of the box would determine if that is the most suitable.
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