Zac Efron is trading red carpets for rainforest life in Australia, where he is building an off-grid home that relies heavily on hemp. The project is shaped around comfort, self-reliance, and materials intended to lessen environmental impact. What happened? Mugglehead reported that Efron is developing "FutureCave" on 128 hectares of rainforest near the New South Wales-Queensland border. The retreat is reportedly six years in the making and is bei…