One trick I learned many years ago was the "checking the tire pressure" move. You just squat down by the tire and play with the valve while peeing. For emergency use in crowded areas only. Works best off pavement. I've also just sat on the step in the slider and went on the side of the road or at the edge parking space in a lot. Very rare, but sometimes plans and coffee don't cooperate.
The luggable loo is a good solution, but opening up a used 5gal bucket inside the confined space of a van will result in a stench that will seep in to the fabric for some time. I guess the best way to deal with the 5gal bucket toilet is to have several layers of plastic bags (kitchen garbage bags) inside, and tie them off after each use. The older bags get sealed in the newer bags with each use; toss asap, but NEVER ON THE ROAD, ALWAYS USE TRASH CANS. There's already too much litter from the self-centered or mouth-breathing portions of the population.