We spoke to an old school trailer restorer and he recommended 5 coats of amber and 2 of clear, so that's what we did.
The result is still pretty light, but we like the contrast with the darker ash cabinets and the birch should age over time.
This round of finish, we used a $2 home depot foam applicator with a jersey knit fabric on top. It allowed us to apply the shellac quickly and evenly and we could store the applicator in a ziploc to reuse later.
We also sorted through 40 sheets of 1/8" birch plywood to find the 6 that we needed for our ceiling.
Instead of twisty nails, we are just gluing up the rafters and then pre-finishing the panels before installing. This will let us get the trailer together in a long weekend, and be structurally sound in the face of the crazy weather we've been having.