I have the aluminum Trailex Trailer and have trailered our boat on several long trips without a problem. Flying Scot sells Tie-down centerboard wedges made out of wood or plastic. I have been using the wood ones. Basically it's two 1/8 inch (or so) thick pieces of wood that are screwed together at the top and have carped glued on the inside for padding. You lower the center board slightly, stick the wedge in from the top of the centerboard trunk and lift the centerboard until it fits snug. The wedges just prevent the centerboard from swinging/vibrating and hitting the centerboard trunk wall.

I wouldn't lower the centerboard and have it rest on the trailer. I think a bumpy road would do bad things to it. Removing the centerboard really isn't an option either since it's quite heavy. So I reccomend just to leave the centerboard up and have a wedge of some sort to keep it from vibrating.

An alternative to the wedge is to use some old mainsheet and cut it in a 1 1/2 foot lenth and tie a big knot on each end to prevent the line to fall into the centerboard trunk. Now just lower the centerboard put the piece of rope between the centerboard and the centerboard trunk and lift the centerboard up like before. One piece on the left and another on the right so that you are using two of the cut and knoted pieces of rope. Keep the knots out of the centerboard and don't go crazy with pulling the center board up.