I have never tried to pull an empty trailer on the grounds so I dont know the particulars of that.

 I would park ot in the north lot as close to the entrance as posible with a sign on it and make flyers to put up in all the buildings.  You most likely will need to be available on short notice to allow people to see it unless you are going to leave it unlocked.  I dont believe that I would just park it there and hope it is still there in three weeks if you dont sell it.

If you get to the parking lots early enough to have a spot near the access roads, you will be able to show off your trailer to anyone parking in that lot. Purchase the largest "For Sale" signs available at hardware and big box stores, and tape them to your trailer. On the sign, write your cell phone number. Beside the sign, make up a sheet listing your trailer's specifications and asking price. Also state that you are on the grounds and can be reached to show off the trailer, which is left locked. Make sure that the trailer is cleaned inside and out, and looking its best.

Take some photos of your trailer and make up a hundred, one page fliers with the photos, specifications, pricing and contact information. State the days that you will have the trailer at the show for inspection. Buy a package of push pins, and post the fliers at numerous bill boards and poles throughout the show grounds.

Bring your title with you and be ready to deal. Within this forum are many threads about how to transfer funds. Beware of any kind of checks including banks' which can be forged.

I would also purchase a hitch lock for your trailer before you go out there.  Every year there is trailers, tack, golf carts, etc stolen from QH Congress.  We lost a brand new golf cart several years ago.  It was easy to spot, as it was red with chrome wheels on it.  We turned that grounds upside down looking for it.  I'm convinced it went into the back of someone's trailer, and left the grounds.  We never did have it recovered.  Just take all precautions.