I have a Downtube IX NS, and have been using two one-foot lengths of Velcro One-wrap or the 3M Binding tape to keep the bike together when folded. I've folded & unfolded 510+ times over the last year and a half.

one piece holds the frame and front wheel fork (near the hub) together. The other piece holds the handlebar to the rear rack. I take out the handlebar completely when I fold so I have the narrowest fold possible (for the Amtrak ride).

For rolling around I have found it easiest to roll it only on one (rear) wheel; I grab the front of the seat and tilt the whole thing back w/ one hand, and I have found it easy to roll, balance, and steer it just with the one hand.