In Australia you have humidity chances that most in other parts of the world can not imagine. It comes down to building the tops out of materials that are not effected as much by humidity and what ever it takes to hold the lids from warping. Have you considered immersing the lids in paraffin wax to seal them against moisture? For what it is worth For me in my area I don't put anything on my hived to hold down the covers or worry about warping. You need to figure out what you need foe your area