The FAQ section addresses a lot of questions including tires and has pictures of various hookups. http://www.cruiserlift.com/swivelwheelfaq.html
I don't have one of these...but it WAS developed as a 5th wheel solution to eliminate the problems and legalities surrounding towing 2 trailers. Worth a read if you face this problem like the OP I think.
I may be adding their #58 model to a class A if the standard class 3 hitch can't be beefed up to carry a 700 lb. load on the tongue from a 2 bike carrier and 2 scooters.
I am presently hopeful of adding one of these:
But the swivelwheel WILL work for me if this does not!