Here is one of the many tutorials, Im betting you have already seen,
http://forums.mtbakervapor.com/t/a-simple-way-to-wick-a-subtank-mini-rba/541
When I got the Subtank mini I was going to spend a day playing around with different coil builds, but ended up spending the day looking at tutorials and learning to wick, lol.
My problem was, I was trying to stuff to much cotton through the coil. To thick and maybe a little to short.
I started making a little longer, slightly thinner wicks so they rest at the bottom of the wells and would lean against those holes in the barrel, basically plugging them holes in the barrel.
I use 50/50 store bought ejuice, and my DIY is 60vg/40pg. Haven’t had any trouble, but would expect to have problems with thicker juices.
The two stock coils that came with my STM, the cotton was so thin I could actually see the coil, and they both leaked like a sieve! I have read several posts speculating, that KT was a little chintzy with the cotton on those.
The beauty of an RBA is that you can make adjustments so they will work with whatever juice you want, make flavor, make vapor...
I bought two KF clones,
https://www.vaporrange.com/ProductDetails.asp?ProductCode=EHP-KayfunLitePlusV2
Wife commandeered the first one, so had to order a second one for myself, they are fantastic, at home, and she has no problems with the KF in the car.
Maybe not exactly plug and play for a driver, farmer, heavy equipment operator, or any other environment with vibration, variable Atmospheric Pressure, G-force...