Restroom trailer for October 2026 wedding: how to keep it warm?

We're planning an outdoor wedding for October 2026 with about 100 guests, and we're renting a four-stall restroom trailer. The ceremony and reception will run from late afternoon into the evening, and it gets pretty chilly here that time of year. The trailer will be placed on level grass about 50 feet from the nearest power source, and a service truck can access the site easily. We're serving dinner and alcohol, so guests will be using it all night. I'm worried about keeping the interior warm and comfortable, nobody wants to shiver in a bathroom. What heating options work best for a restroom trailer in cool weather? Do we need a dedicated generator, or can we run heaters off the venue's power?