Never never never never use FastTech......of course that is my opinion. I've used them 3 times and everything takes forever and when you finally get it, it falls apart. Junk! Again, my opinion.
The VTR sounds good. I have an iclear 30s that I never use with a few spare coils. Don't know how to get it to you, but it will fit robobob's VTR.
About the juice cracking tanks, that is more likely to happen in bottom coils or top coils. The heat is really intense on that short coil. A cartomizer tank has a long vertical coil so it produces less heat and with the poly fill surrounding the coil and an aluminum body then the juice in the tank, you probably won't have the same affect.
But again, that's my experience. Everybody has a different style and preferences when it comes to vaping.