High-rise site in winter: will porta potties freeze on upper floors?

We're starting a 12-story build in Chicago, winter temps dropping below freezing. The first six floors are open concrete with no heat or walls yet. I've got 80 guys on site for 10-hour days, six days a week. The rental company dropped off six standard units and one ADA-compliant unit, all placed on the third and sixth floors for now. No flushing units or restroom trailers up there, just the basics. I'm worried the holding tanks and deodorizer will freeze solid if we hit a cold snap. Has anyone run high-rise sites in winter without heat? Do the standard units handle it, or do I need to switch to something else?