Which holds better contained by polycarbonate (lexan)- electrical device screw or sheet metal screw? I'm building a corner shower seat for my handicapped father and...

I'm building a corner shower seat for my handicapped father and I'm making it out of polycarbonate. I plan to attach the polycarbonate panel together with plastic epoxy and screw. When working with polycarbonate, will I grasp better holding power treating it like metal, and rhythm (threading) holes for machine screw (I'm using 1/2" polycarbonate, so I'd probably use 1/4-20 machine screws), or would I grasp better holding power in polycarbonate only just drilling tap holes and sinking sheet metal screw?
What would you do to perceive cold?
Answers:    The sheet metal screw will tap itself and the threads are deeper and would be smaller number likely to verbs out. You might want to look at MDF screws.

If it be me, I'd drill clean through and use a horse-drawn carriage bolt with one of those self locking nuts. The finishing thing I'd want is for dad to entwine up on his *** from a screw pulling out.
Can I replace the plug on my wash...
Use the correct cement and 1/4-28 (fine thread) screws. Drill and slap the holes ahead of time.
Drill slowly as the drilling friction/heat can present some troubles in warp.
Suggest stainless stell screw as you are in a drizzly environment. Can you also cement the parts together?
Regards,
Eric