Billow V2, Zephyrus, Goliath ( i've heard the V2 is better but haven't tried it)
All dual coil RTA's.
I use 24 guage kanthal, 6 wraps, 2.5mm id but ohm'ing at 0.25. Just built a pair of coils with 7 wraps at 3mm id ohm'ing in at 0.31 on my Billow V2. Not sure if i could fit a 3mm coil in the others. I haven't tried yet. I suppose if i used 8 wraps with 2.5mm id i'd probably be closer to the .3 mark. Could always try some 25 guage kanthal if the 8 wraps don't fit.