As far as i know Smok doesnt claim it to be a dual capable deck - theres a seperate RBA for that, maybe youre confusing the RCA deck with the dual clapton prebuilt coil...
It called an RCA, but you can put in any coil build you like - single, and yes dual (with some fiddling) - though i wouldnt
Its just called a RCA because it has a little more room than some build decks so you can whack in a decent size clapton, comes with a prefitted clapton and mostly to be a bit different in marketing.
I run my bog standard 3mm inner diameter single stainless steel coil in there in temp control mode
I did try the prefitted clapton, but didnt like it, mostly as it was kanthal and i prefer to do temp control....
Free tip, unlike most build decks where you would cut the wires flush at the posts, either you need to have snips that can really cut flush, you will need to pretrim the legs before final coil fitting and screwing the coils in, failure to do so will result in a short with the chimney sleeve - theres not a lot of distance between post and chimney sleeve on the build deck. I dont have flush cutting snips, so i found the short thing out through experience.. I make the coil, sit the legs in the slots, and then one after the other lift the legs up and trim them so they dont stick out past the outer edge of the slot...