"Despite being frankly terrified of him when he loses his shit, I owe it to baby to be brave..."
Nope, Mystery, you owe it to your baby (and yourself) to be safe.
And I don't think that your baby (or you, for that matter) will be safe around someone who flies into terrifying rages when asked to behave like a responsible adult. As others have already pointed out, a lot of marital abuse begins either during pregnancy (when the man thinks that he has a woman trapped) or during the first few months of parenthood (when the man believes that he has the woman trapped because she'll instinctively want to keep her family unit together). And the more that he finds himself getting away with... the worse it will become.
You've admitted that you're terrified... not scared, not made worried by, but terrified... of your own husband.
That's not good.
That's not what marriage and/or a healthy relationship is supposed to be about.
That's certainly not what being co-parents is about.
"... As is said every day on MN, what my DS witnesses will form the blueprint for his future relationships and I don't want him growing up thinking our current dynamic is normal because frankly he would grow up to be a total prick."
If you allow this current dynamic to continue, your DS will grow up to not only think that his father's behaviour is completely normal/how men are supposed to behave (because you're right - your husband will set the markers for your baby to follow), but he will also grow up to believe that women are meant to live in fear, just to keep the peace and avoid the "pissyness".
Unless something drastically changes, Mystery, your child will believe that it is acceptable to bully women. To mistreat them. And no matter what you say, or do in an effort to counter that effect - if he grows up watching you allow your husband to terrify you, to bully you, to shout and scream and rant and rave... until you give in/up for the sake of a quiet life/family harmony, then that is how he will treat his future partners. His girlfriends. His wife. The mother of your grandchildren. Who will then emulate their father's behaviour, and so the cycle will continue...
Please break this cycle that you're in, Mystery. If not for yourself... then for your baby. Teach him that women are worthy of respect, by first respecting yourself enough to either issue an ultimatum to your husband that he seeks help and works to treat his issues... or by (and I hate to say this, but sometimes... it's necessary to do so!) leaving him. Because, and I say this with all due respect, your baby is worth better than this horrid situation he has been born into.
You deserve better.