For some reason, you almost never find a Right On trailer for sale used. The only ones I have seen also have a boat and dolly as part of the sale package. Beldar's suggestion (to look on the Laser Forum) is a good idea as these trailers can accommodate Sunfish or Lasers (or any boat that fits on a Seitech or Dynamic dolly.)
This is a very nice looking aluminumn trailer but from the photo in the ad, it lacks the hardware to allow you to roll a dolly onto it. Maybe the seller has this hardware so it can be converted from a kayak flat-bed rig to a dolly rig.