You'll need a blue slip, obtainable at most mechanical workshops. You will probably also require a weight-bridge certificate, but see if you can avoid that, as the compliance plate should have the weight stamped on it and you might find it weighs a lot more than originally stamped and NSW rego price is based on weight (in bands).
Your camper is registered, though you have an obligation to transfer it to NSW if this is your place of residence, though it suits many not to, for price or compliance reasons.