Beautiful model, and I really enjoyed the build log. Very impressive.
A neat trick we used to do building cardstock structures for model railroads is to emboss the card first for a corrugated metal appearance. Very easy to do, the hardest part was finding the right mold. If you find something like the lid to a peanut butter jar, with plastic corrugations, maybe slightly bigger than your finished piece, tape your cardstock good side in over this (don't worry about the curve, it is not an issue) with drafting tape, or masking tape. Run a pen up each corrugation. Peel off, trim to size, make your bends, and glue together. Foil backed paper, like they use for the bags inside some cardboard boxes of food, gives a very nice metallic finish as well.