See my posts in the Downtube and other posts by Sesamecrunch and Maunakea. We're basically after the same things you are and have/want a Downtube modified to our particular needs. I'm finding that my Downtube Full Suspension can fold to large suitcase size, especially if you remove the "handle" underneath the bottom bracket. This allows one bolt holding the rear shock to be easily removed to allow the rear triangle to pivot and make the fold pretty compact. Worth considering as the downtube is a damn nice bike right out of the box. Needs re-geared for more speed though. Just my .02. Good Luck