You could put the RCS pods just attached to the second stage in a way like the Apollo service module. However, from the extensive size, classic or common RCS wouldnt do much, im looking forward to that update! in the second stage, now i love truax's rockets, and i made a concept of a reusable second stage, it would have clam style fairings (i dont know how to explain it), and where the auxiliary engines either have retractability or just tucked in where a door can close shut it for reentry, while the main engine would retract back, and that a 4-way clamstyle heat shield would extend. Close shut, basically the main heat shield, i don't know how to explain it well, but it's like since the second stage engine is mostly hidden inside, as well as the heat shield. i couldnt do such thing to the aux and 2nd stage engines that instead i bp edited them to be invincible from reentry, i didn't add any rcs pod too, but i did manage to make a reusable fairing, im still working on it though since its a bit faulty (no i didnt make a new extension mod, i just did it on build). are you planning to make a fully reusable sea dragon if you mind if i ask?