I can see emptying the unit for the night but if you are say rolling down the road a few miles to another stop that emptying would be a hassle.  I’ve read about the food trucks in CA and NY about how they do a lunch time crowd and then move location for say a night time gig.

I am sure there is some sort of lid and I am sure the fryer manufacture knows more about this type of thing. I’ll keep poking around and post back what I find.

 
I saw a glimpse of an odd looking fryer on a tv show the other night….it was unusally deep, looked like it was 24 inches deep but had about 6″ of oil in it.  It was on a truck and I wondered if that design was simply to allow for the movement of the truck while underway…….