clutchd, I use Pit Bull Trailer Restraints. Website
The bike in the middle I had on a Baxley Chock at that time. Since then, I have got pin to fit the R6 too. So, all three bikes are held firm. I have an '02 CBR1100XX, an '06 CBR600RR, and an 07 CBR600RR that all go in there. This trip I was transporting our friend Jennifer's R6.
They are super stable. And you only need to strap the front lightly to keep it from bouncing around. No fork compressing! Pricey, but a man man loading job that is rock solid. Bikes never move.