OMG, your quilt is gorgeous! Surely a winner.
First you need to find out the minimum size of the sleeve, the quilt show will tell you.
The shows I have entered it is a 6" sleeve so i make a tube out of 12 1/2" of fabric by the width of the quilt less a few inches.
I always sew my sleeve on. If the quilt is already bound I put the top part of the sleeve up against my binding line. I use the same stitch I would use for applique and my binding and I check the front constantly to make sure my stitches are only going into the batting and not coming through the front of the quilt.
Good luck in the show and have fun! I love, love, love your quilt.