I think you are trying to get out of the house as cleanly and while doing the least harm possible. My take on how to do that:
Cleanly -- I see the best thing there as being firm and consistent in what you say to him, not giving him mixed messages. (I've been the recipient of things that felt like mixed messages to me!)
Do you know if you are moving out to end your marriage, or moving out with hope of saving it? If you are certain, communicating that to him should help.
Safely / without causing harm -- I don't know enough to advise you on that yet... .so more questions:
What do you expect him to do if/when you tell him that you intend to leave?
What would you expect him to do if/when he comes home and finds you gone?
What ACTIONS are you afraid he would take?
- Physical violence as you leave?
- Emotional/verbal violence as you leave?
- Keeping your car?
- Preventing you from getting your stuff?
- Damaging your stuff?
- Stalking/harassing you?
- A suicide attempt?
Start with the list of things you are concerned about... .once you have the list, work on a plan to deal with or prevent things.