In fourth seat, after a 1NT response, bid as if you were in second seat!
Just one difference, your han must be a little bit stronger, that's all! (The responder might very well not be weak.)
- The Michaels are the same.
- The takeout double promises 4 cards in the unbid suits with a hand which is a little stronger than if it was made in second seat.
Careful! Your Partner, who has already passed, might have nothing! Take the vulnerability into account.