Put it in Park both on a trailer or when flat-towing it. When flat towing a TJ the transmission must be either in gear or in Park and the transfer case must be in Neutral.
I strap to the axels for primary security and then to my bumper shackles to control body movement. With just securing to the body I’ve had straps come loose after hitting a large hole that came up from nowhere. Mine are sticks so 1st gear and 4 low.