I used a regular inner cover with a notch this year, with the telescoping cover shoved close to it to keep things out but allow some airflow. I use wooden covers, we have had bad experiences with plastic ones.
Some locations have serious moisture problems, others have none, it's one of those "all beekeeping is local" things. If you don't have evidence of moisture in your hives (damp wood, mold on the frames, etc) you don't need more ventilation. If your hives are wet in the spring, you need more, but you also need to avoid a hurricane howling through the hive in the deep winter (if you have deep winter). The more tightly sealed the hive is, the more important good ventilation is, of course, same as your house. Around here, a screened bottom board with the sticky shoved in and a partially closed top entrance slot in the inner cover is prefectly adequate. In the fog zone on the west coast, this would probably result in soggy hives.
Whatever you do, I strongly recommend wooden covers that are un-finished on the inside (no paint, stain, or sealer of any kind), and if you have severe condensation problems, a condenser (a shallow with a screened bottom filled with coarse sawdust, chopped leaves, or something similar) on top of the cluster. Plastic outer covers, painted surfaces, or metal exposed to the elements will condense water that will collect on the surface and drip. Wood will absorb quite a bit, and it will move through the wood and exit the hive rather than collect and drip. Dripping cold water kills bees!
Peter