"Marine/RV toilet paper" is just...
cheap institutional grade toilet paper marked up to 3-4 times what you can buy it for at the supermarket. Don't use premium toilet papers--Charmin, White Cloud, Northern etc...they're full of extra fibers for added strength and creams for softness. If you have any doubt about whether a particular paper is suitable for use aboard, tear off a sheet and put it in a glass of water overnight. If it's still a whole sheet in the morning, don't use it...but if you stir the water and see "snow," it''s just fine for use in marine sanitation systems.