I have a few poly hive boxes that are 33 years old , so they seem to last !
In the winter the air is cold and DRY , we ventilate out through the hive bottom , yes the walls can get frosty , haven't had any hives freeze shut , but dead bees can reduce ventilation so I use a high bottom board , a bout 8 cm under the lowest frame . It is ok that the walls have condensation as long as the bees are dry.
I don't know if poly hives work with top ventilation !?
We use big boxes for brood and 3/4 langstroth for harvesting , they way about 17kg , don't forget to bend your knees ;)
If you have poly hives that have become yellow from UV light , wash and brush them clean so they become white and give they a coat of paint and they will last many more years.
mvh edward :-P