I use a bike grab (
http://www.bikegrab.com/) bolted to the floor of my van and some ratched straps attached to the frame to stop the back end bouncing around. It's not going anywere. This is ok if you get regular use of a van
As mentioned in earlier posts make sure you compress the suspension to stop the bike bouncing around, put a cable tie round the front brake, use the frame as a anchor point for any ropes or ratched straps but not the wheels as they will move and the ties will work loose and cause the bikes to move. Good luck with getting all the bikes in. The 2 one way and 1 the other is the best way.