Yeah, asset managers generally advise withdrawing no more than 4% annually to preserve wealth. However, I'm guessing that this is classified similar to a foundation, which must pay out 5% of its assets each year.
EDIT: Just read the wikipedia article he links to, and as the value of the trust is recalculated each year, and his annuity is based on the recalculated value (as opposed to the original value) it's effectively impossible to deplete the value.
Also, you can setup a net-income CRUT that pays out the lesser of the annuity income percentage, or the trust's net income for the year, thus ensuring that your annuity doesn't reduce the value of the trust from year to year.
EDIT: Just read the wikipedia article he links to, and as the value of the trust is recalculated each year, and his annuity is based on the recalculated value (as opposed to the original value) it's effectively impossible to deplete the value.
Also, you can setup a net-income CRUT that pays out the lesser of the annuity income percentage, or the trust's net income for the year, thus ensuring that your annuity doesn't reduce the value of the trust from year to year.