I'm just trying to get more details of what's going on with your rabbit so as to better know what type of product might be needed for the situation. Could you go into more detail. Does your rabbit have urine scald or something like that?
Applying a moisturizer after a butt bath isn't required or necessary, unless you have bare skin because of fur loss, and that skin is either showing signs of irritation or is at risk of becoming irritated because the problem causing the fur loss hasn't been resolved yet, and so the skin continues to be at risk of ongoing irritation. Then if the skin is sore, is there a bacterial component that requires the cream having an antibacterial in it. If there isn't fur loss, you can't really be using a cream, as that means the skin is probably fine, plus it will gum up the fur.
So I just need a little bit more clarification before I know what to suggest.