Weeeelll...
If a 2-3 gallon portapotty holds enough to meet your needs, I see no reason why it should be a pumpable model. Otoh, if you have to take it ashore more than once at end of each outing, it's worthwhile to consider installing a larger 5-6 gallon pumpable model (the only difference, btw, are some fittings on the tank that allow it to be permanently installed for pumpout)...'cuz a full 2-3 gal. tank only weighs about 25 lbs, but a full 5-6 gallon tank weighs 40-50 lbs--which is a lot to carry off the boat and up a dock to a bathroom to dump, but easy to pump out. So far from complicating anything, it simplifies. As for your questions about frequency of visits...I'm not a doctor, nor do I play one online

...but I can tell you that the average number of trips/day to the bathroom for adults is 5. If you have to make 15 trips--3x the average--I suggest you do see a doctor. No holding tank--portable, self-contained pumpable, or full size remote--requires the use of any sanitizing chemicals. In fact, there are no holding tank product that sanitize the contents...odor control/elimination is the sole purpose for any of 'em, and all any are capable of doing. And yes, if you want to prevent odor, you do have to use one of 'em.