Kiss. Keep It Simple Simple. Nothing simpler than a wag bag. Any kitchen garbage bag will do. They sell fold away toilet seats on eBay that tuck away when not needed. Unfold seat, place garbage bag over seat, with puppy pad inside to absorb liquids, and tie shut when done. Deeper bags, can be twisted several 360 turns, then placed over its self again before tieing bag shut. Double bagging with one bag. Place in any dumpster that would also accept a diper. All trash sacks today break down, so you are not making a time capsule for tomorrow's anthropologists. Lol
If you had a dedicated head area, some of us have come up with fancy ways to use and store wag bags. Mine looks like a home toilet. Back tank stores new and used wag bags, rather than water.
Advantage of a wag bag, done correctly, is there is zero clean up. Odors are locked in the bags, and never a issue of dealing with pump outs, or toating a portapotti around to empty it. I added one of these to my RV garage. I never use the tiny toilet in our bedroom. Too crampt.