I have a Titan tube mod that works amazing. Nice hard hitting mod. The Karma mod from Geekvape is a good choice too. It has a quite cheap pricepoint and a good hard hitting mod. I believe that it is hybrid though, so you will want to make sure that the 510 pin on the Freakshow is safe to use on it.
Just a heads up, I believe I've heard that the black version of the Freakshow V2 is painted inside as well as the outside. I've read a review of a guy who bought one from a local B&M and the paint started to melt on the inside from the heat of the coils.
I'm not worried about that the owner at my local vape shop only sells the ss version and on my reuleaux rx 300 been working great but been wanting to get a mech mod for it mainly for looks kinda looks like a nipped on my rx 300
If you would be game for a dual battery mech, I have been LOVING my Noisy Cricket II-25. It would look and perform phenomenally on that. I know you said a single 18650, but still thought I'd throw that out there.