I ran your exact setup back in 2015, (Subtank Mini, Istick 50) but did not have access to the 30x2+38 that
@r055co recommends. However, a 28X2 + 32 Clapton will fit, but the clamp-down screws can be problematic. Those posts and screws start to feel a bit flimsy, like you're going to break something before it's clamped down tight enough (though I didn't break it). If you like your coil down low between the posts, you're pretty much limited to 2.5mm id, but you can position a 3 mm up higher. So, a Clapton will fit but it's not really the ideal deck for such a build. The main issue I had was not with the build itself, but with the Subtank's limited juice (and air) flow. When I ran a Clapton in it, I had to keep dialing down the watts to where it could keep up, which kind of defeated the purpose of running a Clapton. I did have a decent run with the prebuilt Clapton that comes with the Protank 4 that I popped in my Subtank on a whim (specs unknown).
My preferred build was rather vanilla; 24 or 26 Kanthal (3mm id, positioned slightly above the deck), .45ish ohms, Rayon wicked, in the 30-35 watt range, which was about the highest watts I could manage with any build on this tank (juice flow). For this tank I built for simplicity and longevity, because it was one of my traveling tanks (trucker). But I rather suck at building, so I'd follow the advice of the wizards here before mine. Just wanted to chime in that it is possible to run a Clapton on the Sub.
