I'm not an expert or anywhere close to it on this subject. I can tell ya that I do have the hypervent all around the mattress (including the sides). I also run the overhead vent on low with it cracked open a slight bit. The only time I had condensation around the bed was one of my first times out camping and forgot to turn on/open the Maxx fan/vent. It was raining outside both days/nights. The next night I didn't have any problems.
Now, as to whether that was the hypermesh or the fan, or both (or the stars were aligned properly
), I could not tell ya. I do know we decided to get it just like you do insurance - hope you don't need it, but when you do, it's worth the investment.
I got mine in a big roll from a marine supply store in Seattle. That stuff was a fricking PITA to trim to size. Forget using scissors. Or a box cutter. I ended up using a hot knife/blade and that worked lots better. I also cut it on my 6' folding plastic table where it didn't matter if I got gouges or what-not on it.
I also put it under and behind the dinette cushions, although I was told later I didn't really need to. Well, I feel better having it on there - just in case and all that.
Most of my camping has been along the wet Pacific NW, so I figure it's better to have than to not have it and have to start replacing the mattress and cushions as they got icky and moldy.