I keep seeing these walk in bathtubs advertised on tv commercials. They
have a side that opens like a door. THey are intended for the elderly.
The concept makes sense, because I am aware of how difficult it is for
elders with health issues. However, I find it hard to understand how
they can seal those "doors" on the tubs, to be water tight. And even if
they do have a good seal, how long do they last?

Like the door seal on a refrigerator, car door, etc, they all seem to
fail fairly fast. But for a bathtub, there is a lot of pressure against
that seal. I'm not sure of the water capacity, but even 25 gallons
weighs about 208 lbs (one gallon is 8.34 lbs). That's a lot of weight
against a gasket/seal. And I would think they hold more than 25
gallons.

Of course if the gasket fails, that's a lot of water to flow on the
floor and will cause a lot of damage.