What is the best way to attach the sill ? The attached pic is a mock up I’m doing on a 4′ wide window, but I also have 10′ wide window/door openings. On the rough opening I have flashing tape / sill pan. I plan on using vertical grain 1x cedar for my sill. 

My initial idea is to lay beads of compatible adhesive and add a few screws w/plugs to hold it down and keep it from bowing out. The sill flashing is Exoseal and not so stretched in the area for the screws.