how can I protect my portion of a family trust if my divorce is not final?

I agree with the other attorneys that while you are alive, your husband will not be able to get anything from your inheritance. However, you should also be aware of the following: if something happens to you after you receive the distribution, then your husband might be able to get this money as his inheritance (i.e., legally he would be your surviving spouse).

I doubt it.  But the one way to be certain is to get the paperwork completed, get the divorce now.  I'm not a California lawyer, but in most states, the date you file for divorce, with a few exceptions, is the cutoff for property to be part of the "pie" that gets divided, whether it's community property like your state, or equitable distribution as in others.

One thing that's true in most states, also, is that if you keep inherited money or property entirely separate, it will also be exempt from your spouse's claim.

If there's enough money in that trust to worry about this, it's worth hiring a competent attorney.

Depending on just how the trust is set up it may be considered to be an "inheritance" and therefore separate property. 

Property acquired during marriage by "gift, bequest, devise, or descent" (i.e., inter vivos or testamentary gift or intestate succession) is the acquiring spouse's separate property. [Ca Const. Art. I § 21; Ca Fam § 770(a)(2)]

Frankly, this can be a grey area of the law.  Obtaining a divorce before any distribution of the trust proceeds, however, will make the situation clear cut.