Is it legal for me in NC to set up a trust giving away our marital funds without giving my wife an express declaration until after we have signed a separation agreement or after the marriage has ended? Will the trust be valid? Can she still claim half the trust?

Regardless of how you have marital property invested, if it was acquired during the marriage and there is no prenuptial agreement that protects the asset in question, it will be considered marital property and is subject to division. In other words, placing marital funds in a trust does not change the fact that they are marital funds; you can’t shield the asset by placing it in trust.