An afterthought of a more practical nature as well:

I have spent years of my life living in and around the camper/RV/Van life scene and many,many thousands of porta potty encounters later I offer this advice.

Secure that thing to the floor somehow. or pen it in with heavy things, or at the very least make sure its empty before getting underway. One good toss on a stormy sea and you'll be swabbing that deck of nasty spillage.

I've seen this on land in RVs that merely hit a speedbump. I'm quite certain the sea's speedbumps will be more severe.

Just a thought you probably already thinked. But it was worth mentioning when I saw the photo of the unsecured throne just waiting to make your day a little bit messier.