Get a bigger pair of channel locks. If you have a hammer/ flat head if your membrane has raised sections you might be able to give it a little love to loosen it up but your going to maul up your plastic and run risk of damaging membrane
Use a standard belt. Loop it around and through the buckle and use it like a wrench. If it slips, reverse the direction that you wrapped it. Have used this methods in oil filters back when I changed my own oil.