This might giive you some more options.

 

I wouldn't use the saddle bag rails .... they WILL bend ... I would recommend a soft strap through and around the rear wheel ... just my .02 cents worth.

 

If you want to make this easy get the HD or Kury fork mounted tie downs. They look good and bolt to the driving lights mounts. Makes it quick and easy to hook up the strap.
The passenger floorboard mount works good to keep to rear from bouncing and are easy to access.

 

I have an Ultra Classic that I tow in an enclosed trailer and also have a Condor chock which has been great. The trailer has tie-down points built into the floor. The bike goes in the chock and gets secured from the rear tie-down points to the passenger foot rest bracket. I also put two tie-downs in the front around the shock tubes for some added security. All the tie-down straps are soft ties. Between the 4 rachet tie-downs and the Condor the bike is in solid and without having to compress the suspension. I've towed a long way this way and the bike never moves from where I secured it.