Heh. The smallest dual 18650 box you're gonna find will probably be something in a Hammond 1590 enclosure, which isn't really that "small" by any means. It's physically impossible to fit two 18650's into a iStick-sized device.
I recommend something like a Sigelei 150W. Personally I love it, and it'll provide you with more than enough power -- probably for a decent amount of time too, especially at 20W.
I also own a IPV3 (not the 4) and I definitely recommend the Sig over the IPV. 100%.
Actually I'll talk about all my boxes:
I have two OKL-T20 Hammond-style boxes. One's a custom-made one (currently out of commission) and one HexOhm V2 VaporShark edition. Love 'em, they're my daily driver. The OKL-T20 chip is DIRTY-nice. I've heard it underfires (5.8v instead of 6v?) a little, but whatever, it's consistent enough for me.
I have the IPV3, which is really just a backup unit at this point. I hate how it fits in my hand, and the buttons aren't nice to press.
The Sig150 is VERY nice for a mass-produced device. I have not been disappointed in it, and it serves as the "take it to a party in case you get too drunk and lose it" device. Only 100 bucks, compared to my OKL boxes that's cheap.