I believe R30 fiberglass insulation is approximately 9 inches thick. If I am correct, R30 insulation between 2x8 rafters will not allow proper ventilation. This does not meet code. Warmer air can hold more moisture. No problem with condensation there .
Condensation is a problem of warm wet air being cooled below the dew point.
If the house is air conditioned and is cooler than the outside, then you have a problem because the warm wet air will be cooling inside of the insulation. There is differences though. There is a much greater temperature differential with a glass of ice tea which is at 32 degrees F sitting in 85 degree air. I don't know if you need moisture protection for AC spaces in warm wet climates since I've never worked in such a climate. I don't think it is a problem to the degree that a warm house in a cold climate is.