I have a 1976 Morgan out island sailboat. The original ports have been replaced. Apparently the old ports were cut out and smoked lexan or plexiglass was cut to size and screwed on from the outside. There are 3 rectangle pieces on each side. Over the years they have cracked and I would like to replace them. Previous owner said he used the wrong material and because of heat and exposure and flexing of the boat they have cracked. What material should I use to replace them so this does not happen again?