Best deodorizer for high-use holiday event porta potties?

I'm coordinating a holiday festival with about 5,000 attendees over a weekend. We'll have 20 standard portable toilets and 2 ADA-compliant units on grass near the food vendors, with alcohol served. The vacuum truck can reach them easily. Last year, the units got overwhelmed by Saturday afternoon, strong odors even after the morning service. I know heat and heavy use break down the deodorizer faster. What's the most effective deodorizer for high-traffic events like this? Should I consider upgrading to deluxe flushing units or adding more service visits?