I figure it should be ok if I use a good waterproof adhesive and glue the entire surface to the skin. A few staples here and there should do the trick. The leading edge of the trailer trim will be a bit higher than the shingles to prevent wind lift on the edge.
Hope to be closing the deal on an old popup this weekend, so construction may actually begin this year!

If you folks have any pics of such an installation, I would love to see them.