Expect to reduce moisture lost, don't expect miracles
Rhodies in the wind
If you have broadleaf evergreens in sites that are exposed to
drying wind, or with root balls still too small to provide for the
plant through winter, you might set up wind screens now, and/or
apply anti-desiccant such as Wilt-pruf® or
Moisturin® on a mild day.
Don't expect miracles...
...from these products. They block pores on the leaf surface so
that less water can escape on mild winter days -- water that might
be irreplaceable while the soil is frozen, and result in scorched
leaf edges and dead twigs. Yet they can't do anything to make a
plant more hardy. That's a result of genetics and health.
To increase a plant's hardiness
Put your effort into watering it well, if it's in a dry place,
increasing its light if it's too shaded, or improving the drainage
if it's a species such as Rhododendron that suffers when
there's too much water and too little air around the roots.