Another great option for you peeps trying out the kayfun configs is the rounded bell cap.. It also connects via an o-ring and not screwed into barrel... with this one you DO use the nano chimney cap. It's one of my favorite configs without doubt.
$1.69 Acrylic Kayfun Bell Cap - yellow at FastTech - Worldwide Free Shipping
There are more colors, some come with o-ring, some don't so grab some of these o-rings for backup:
$1.71 Silicone O-Ring Seals for Atomizers (50-Pack) 50-pack - 8mm*5mm*1.5mm(OD*ID*W) at FastTech - Worldwide Free Shipping
And a chimney and cap (if you don't have already):
$2.26 Replacement Five Pawns Styled Chimney for Kayfun RTA - stainless steel at FastTech - Worldwide Free Shipping