ditch the cables and ratchet straps.
position your crossbars directly above the 4 corners of the lights. use zip ties to attach each corner independently. you could use extra zip ties to give yourself more adjustment or just one set and have it an inch off the ceiling. just account for airflow and make sure it's not heating up the top of your tent fabric. I did this with an HLG65 in a 2x2x3 for a long time.