Important: Perspex is prone to crazing if misused.
Do not use countersunk screws. The material is under great stress, as the wedge is pulled up tight. Perspex eventually cracks from a countersunk screw.

If the hull/superstructure is curved the Perspex is put under a great strain as it is pulled round. Minimise the stress by using the thinnest practical sheet. If the curve is very tight it is advisable to have the windows formed to the correct curvature. This should prevent crazing which is almost inevitable when the material is greatly stressed.

When drilling make sure that the hole is chip free. A chip provides a point for "crack propagation", which will take place very quickly when bolted up. If you have grinding facilities, regrind your drill to zero rake so that it "scrapes through" rather than cutting. This will minimise the likelihood of chipping.
Don't over tighten bolts/screws. 5. Keep your windows clean with warm soapy water. Don't wipe when dry, as grains of dirt and sand will scratch the surface.