This is a resurected thread, but Ill throw my $0.02 in case someone else is looking for ideas. I have used our Cougar sliding rear rack for bikes on the few trips we have taken since we just got the 5er this season.
First off I removed the spare tire and holder and installed a BAL hide a spare to store it under the trailer, works great. I cut a pool noodle and used a little duct tape to hold it around the pole that comes up. Then I used racheting strapes through the wheels at the bottom of the rim and around the platform. Each wheel is solidly secure. Then I use another racheting strap through the frames and around the pole. Then I use a thick cable through frames and around trailer frame and lock it with a big frame lock that I have. I wouldnt leave them unattended as a crook with a battery power saw would have the bikes in 30 seconds...but for transporting it works great.
Bikes are secure and dont move at all...I love the rack. Even without bikes it could be used for lots of other stuff.