The plastic coating prevents any moisture loss. The trees are enveloped in moisture and thus dehydration is prevented. Make sure that your storage area has excellent drainage. Roots will die if exposed to wet conditions followed by freezing conditions. The previous comments are primarily for hardy trees.
Tropical trees require special attention.
Alternatively place your trees under florescent lights. Most members have an insect problem with their tropicals. As winter progresses more and more flying insects appear. Last year I used a systemic insecticide when I brought the trees indoors. There was a substantial reduction in the insect population.