I don't have a V5, but I have several V2 Lites and V3. I also had problems. I knew all along that it was me since so many people absolutely love them. Still, I wasn't having any luck, so I stored them when I discovered and fell in love with the Ego One Mega with the CLR coil. That's still my favorite atty/coil setup, but I kept thinking how I'd bought five Kayfuns ($9.99 each) so I need to learn how to make them work.
Bottom line, I think I was over wicking. I started searching Youtube and came across this video. This guy wasn't putting the cotton wick in nearly as tight as I was. I tried it his way, and it works like a charm. Great flavor in the Kayfuns, now. If you're interested, the part about wicking starts at 8:30 on the vid.
I tried the Lite and a 3.1ES. I still have a couple of V2.1 Minis. They are too tight of a draw for me, so I was constantly "overdriving" and burning. I'm having MUCH better luck with the V3 Mini and the V5.
Mike, you're right - barely enough cotton for a teensy bit of resistance. I actually prefer Rayon for my KFs. I can "overstuff" and still get great wicking. I also am VG-heavy in my juices. Rayon seems to work better for me in this instance.