My county board of health has decided they want to be sneaky to prevent themselves from developing a revenue stream (food trucks).
They won’t license a restaurant/kitchen unless there is an employee toilet room with a hand sink in addition to the already required kitchen hand sink. Permits for temporary or mobile food service requires the use of a commissary kitchen (none for about 500 miles).

I’m putting a porta-jon on a trailer with a handsink and a sign explaining it. I’ll show ’em.

So these are very common among HD, Seattle requires a bathroom agreement with a brick and mortar business to be within 200ft of every stop you plan to make. The thought is that, should you REALLY have to go. Especially, during the time when you should be serving. That you have one available.

Although the idea of a tow behind porta-john is a good ones and would work for a little while. Once that unit is getting full I wouldn’t want to be towing it around sloshing back and forth along the highway. Maybe consider a small Shed/trailer build up with a RV toilet and holding tanks. So that the sloshing is contained to the black water tank. Also out here in the wild west they require a Hot running water sink for the bathroom area in addition to a working hand sink in the truck.