All I run is Abelo poly hives with open mesh floors, never had a damp issue since I started using them over 10 years ago.
Mick, If you are getting damp in your top box using an overhanging roof, then the only source can be condensation from the bees inside the hive. Maybe Teesside bees perspire more in your tropical micro climate than my tundra hardened Buckfast
If you are using the reduced profile roof that sits on top of the new style crown board with no overhang.....then throw the roof in the bin and get an overhanging roof (the old fashioned ones). The crown boards though are excellent as they have a recess for a dedicated Ashforth mini feeder, plus they have a sealable vent that means you don't need a travel screen when moving bees....or you can remove the vent entirely and pin a rhombus clearer board underneath. And for the rest of the year it can act as your crown board..
A simple 4 in 1 design that works really well and saves oodles of spare kit hanging about.
And JoJo it's easier to clean and sterilise poly hives than wooden ones, you simply spray with a solution of bleach, leave for a few minutes (while you spray another box or boxes) and hose off. Easy peasy....