Just finished a build of a 6x12 enclosed and am happy with the results! Etrack is for sure the way to go and wheel chocks are great for single person loading because the bike stands up on it's own while you go for straps. Pictures in the link below.
I bought the trailer and painted the walls pretty roughshod with white outdoor latex paint and did the floor with paint on bedliner before bolting down the e-trax. Did some rubber flashing around the seam just so that I could be sloppy with the bedliner and make sure it covered the floor to wall joint. Marking tape to mark the studs/beams and some LED battery lights. Really happy with it all!