My opinion... it may not be a good idea.
Even if you figure out a sky hook to lift the Hobie's 70 plus pounds (depending upon model) you'll then have to deal with some way to secure it so the boat and the trailer won't get damaged. That means you'll have to invent a roof rack mounting system that will accept a cradle for the Kayak such as the Hully Roller and Mako Saddle combination that mount on Yakima round bars. In my estimation, that would be just as difficult as the lifting phase.
You see... I'm still going through ideas and possibilities of how to properly secure a Hobie on my new Honda Civic coupe; I should have bought the four door sedan.
I also have a Ford F-250 with a lumber rack and an Arctic Fox Travel Trailer. To fit the Hobie on the gas guzzling Ford is pretty straight forward even though difficult to lift that high. The Kayak mounts on pipe insulation foam with the cockpit side down (like a Canoe) because I have no fifth wheel on the back to get in my way I can do that. I went trailer as opposed to fifth wheel so I can pack a quad.
Maybe you could rig a boat loader/rack like the Eide boat loader http://boatloader.com
It may be the best solution to add a front hitch and load bar. Check that out on their website.
I cannot imagine how I would attach a rack to the top of the Fox Travel Trailer. I can visualize the forces that would cause all manner of damage to the rubber covered roof, at highway speed, plus the A/C, bathroom, living room and refrigerator vents would be directly in the way.
Pardon the length of my answer, I frequently get carried away and tell someone how to build a clock when all they asked is: "What time is it?"
Hope you get a solution...