"However, I travel with my wife and this is not an option for various reasons that are not important right now."
Now that opens a can of worms lol.
But seriously, we hit every gas station and restaurant and grocery store and road side pull out. In the morning, we head for the closest one.
My wife and I both hate the porta potties, cassette things, even flush toilets in big RVs that must be dumped. We carry a shovel, plus a frame/seat thing but only use it if we ate something disagreeable..... ps, diet can reduce the need for a toilet dramatically. Research what long distance runners and tri athletes eat so they never need to stop. We are not religious on the diet thing but if a tri athlete can swim 5 miles, bike 100 miles, run a marathon without needing to stop...... it is worth finding out what they eat.
actually what they don't eat is maybe as important