Ought to take a look at Chariot trailers, I've had their single cycle sled 9 since '95 and it pulls great. Used it for my Wing until I got the Valk so you know it will more than handle an I/S or larger. Mine weighs about 425 and pulls at highway speed(65-70) like it isn't there. Loads like a dream, just ride the bike on using the trailer wide ramp. Run the front wheel into the built in chock and let it kill the motor. Before loading, I always pull the side covers off the bike and position the side tie downs so I can reach them, then ride it on to the trailer and hook them to the frame. I can load/unload by myself, I prefer to have it hooked up to the car first....more stable.
http://chariotmanufacturing.com/?page_id=184