We rarely if ever use the flip down seats. My mother (who has MS) is not only a large woman, but has no balance, so these seats with no armrests (and often with the grab rail on her weaker side) are not possible for us. She cannot walk or stand at all.
I have found a better solution is to use the roll-in shower, but avoid the use of a tub bench or built in seat. I routinely go up to the pool area as soon as we arrive and "exappropriate" a pool side plastic chair. We keep it in our roll in shower for the duration, it has armrests, and I can transfer her onto this and use it when assisting her to bathe without ever feeling like we are both going to end up in a heap on the floor.
If you need assistance, it is also best to not bathe when no one else in your party is in the cabin. The story above could have resulted in a serious injury (as when my mother fell off the toilet on one trip we were on and broke both femurs).