I think some tanks are worse than others for leaking. And, I do think the right wicking is going to make a huge difference. I'm not very good at that yet, and for me, it's more difficult than coil building. Some tanks are leakers, some aren't, and it does depend on the design, as well. I have a doggystyle which I really thought I got right, coiling and wicking, but when I went to use it, I found I must have either not screwed the coil down tight enough, or the coil broke when I wicked it. It's been a) sitting completely upside down in its little box with juice in it b) skittered across the room when I was trying to take it apart and couldn't and c) has not leaked a drop.
I'm not saying this is a phenomenal outcome or anything, I'm just saying that particular tank is NOT a leaker, and I DO NOT believe that it's my perfect wick that's stopping that from happening. It's the way it's designed, I think, more than anything.
I'd love to give advice on other, more leakproof RTAs, but I have one working (the Coppervape Hussar clone) the Doggystyle (that I really do want to try using) and a couple others that I've not gotten down completely yet. My fine tremor doesn't help here, but there are RTAs that don't seem to want to leak as much. I am not sure if the seals are doing it, whether it's a top airflow vs bottom, or anything else, other than some RTAs that don't seem to make it their MISSION not to leak, and investigating those is a good thing. I do think the right wicking will cause less leakage/seeping in the ones that want to. While it may SEEM a piece of cotton may not do much, keep in mind that cotton balls are used for other leaks (for example, when giving blood) with the correct PRESSURE. That's sort of how a wick works, to put it in the most unscientific of terms, I'd say.
Anna