Insulation, Radiant and Vapor Barriers - Do I need venting Cathedral ceiling FL Keys?

We only use the heat 4 or 5 days a year (when it gets below 60). We use the AC about 30 days a year because we have a nice breeze and have the windows open most of the time. Since we will not have any warm moist air contacting a cold surface will we have a moisture problem? We have a metal roof with Grace Ice and Water sheild underneath. The way the house is designed it would be hard (but not impossible) to have venting. I would like to put insulation between the rafters when I install drywall as this will make it more confortable on warm days when the breeze in not very strong and the windows are open. With no venting would there be a moisture problem and would the metal roof get too hot and cause a problem with the Grace Ice and Water sheild?

Practicality aside.. check with your local permit office.... They can tell you what is required in your locality.