Salt water generates 'bleach' in the water. In a well maintained pool, there's no odor from either 'salt' or bleach.

An 11 x 20 base is pretty tight, for several reasons. If it was an 11 x 20 concrete pad, it would probably be OK, but that's not what you are talking about.

You probably want a 12 x 22 base that is SOLID, LEVEL, and not sand.