I found that a slice of 1.5 inch polystyrene placed on top of the inner cover, under the top greatly reduces condensation at the top of my wooden Langs. My inner covers have a slot in one end to form a top entrance or ventilation vent. I place the inner cover so that this is up. Next add a 1.5" spacer rim, to give room for bars of candy and pollen, then the polystyrene and finally the top. I'm guessing the candy, polystyrene insulation and vent all contribute to the reduction in condensation. My newer tops have the 1.5" insulation built in, making life a little easier and improving the weather protection for the inner cover and vent.
FYI, you can buy polystyrene tops for 10-frame wooden Langs from Dadant. These seem like a good idea to me, as long as you use an inner cover and paint them :)