Shower Drain

Just about to install my shower base in my basement bathroom. Are the no caulk drain seals reliable or should I caulk around the drain and pipe as well.
Also my drain has to sit inside my concrete floor . I left a square opening to do this in my floor.Should I cover up with concrete or leave it open so if the shower were to leak it would drain through the gravel under the slab.
Any help would be appreciated.

Use the all brass no caulk drains. Make sure the hold down nut is tight.

I would leave a small area open around the drain but not if you have water issues.