I will using rock salt to help control roots in my drain.

I have two choices as to where to dissolve the rock salt:

1 - A fiberglass utility sink in the corner farthest away from where
the drain exits the house.

2 - A fiberglass shower stall about 3 feet from where the drain exits
the house.

I don't care what happens to the utility sink, but I don't want to
damage, stain or in any other manner hurt the shower stall since it
gets used (by me) on a daily basis.

If I was careful about how I place the rock salt in the shower, would
dissolving it cause any damage to the base, which has a "textured"
slip resistant base?