A good insulation for boats is Armaflex sheets. You should be able to find threads on that topic. I am surprised your Catalina doesn't have a headliner. Wasn't that standard on Cats?
As for your condensation problem, you need to reduce the relative humidity in your boat. The easiest way to do that is to introduce more fresh air into the boat, and exhaust some of the moist air. Modifying your heating system so that it draws some outside air into the return air of the heater may help. The positive pressure created by the addition of outside air will naturally force some of the moist air out through a vent or partially open port light. The last thing you want is to seal up the boat tight. Fresh air is the key.
1979 Santana 30 Tall Rig