I installed a handicap shower set up for my dad today

.The little hanger for the hand shower came with screws but my dad doesn't want to use screws because he has one the plastic shower/tub and thinks it'll leak.I know better but I really don't need to be getting him upset at this time.At the moment its on there with the basic GE kitchen and bath silicone which I'm not fond of.
To make a long story short what's the best epoxy for both waterproofness and strength?West System maybe?
I'd wait till Monday and just ask someone at work but I'd like this taken care of asap.