Couple things: Dow 795 is the best silicone to use, it's specifically formulated for acrylic. Don't use 5200, acrylic is about the only thing it won't stick to. The windows will leak if you use it. Second, the screw holes need to be a little bigger than the screw so the acrylic can expand and contract with temperate changes. About 1/4" holes for #10 screws. And turn them in just barely tight. Sight along the edges, if the plastic defects at all at the screws they're too tight. Back them out a little.
replacement of sailboat window after I realized these windows were not available to buy, I had to take sheets of Plexiglas and build my own. not easy just had to be careful .