I have repeatedly ordered (tropical) gardenias from across the world, often around January so these temps are not a problem and they usually come as small rooted cuttings & potted in plastic pots and wrapped in paper bags, these never had any problem and I don't consider them so sensitive to ship.. As for big plants I have had problems when they arrived completely bareroot in wet sphagnum (around 50% success rate) but that goes for most plants...I don't think wrapping it in a plastic bag to reduce weight will cause it serious problems just don't water it too much or immediately before and maybe make some holes on the plastic bag for air circulation. Good luck!