Charles Chauncy was minister of First Church in Boston for decades. He was very influential and is best known as an opponent of the Great Awakening (standing against men like Jonathan Edwards, George Whitfield, et al). So that does not make him an obvious person for an evangelical to turn to for inspiration.
However, Chauncy was a firm Bible-believing Christian and whilst he sadly came to doubt and then reject the classical doctrine of the Trinity we must stress that he did so because he believed it to be unbiblical (it was not uncommon in this period for Bible-based Christians to reject the Trinity as unbiblical).
Anyway, of interest here is that Chauncy became a universalist because he believed it to be the only view consistent with Scripture. ...It's true Chauncy did think Scripture taught both theological unitarianism and universalism; but he also thought the natural law discovered by reason taught such as well. And it was in combining reason and revelation that we arrive at such conclusions. (To some who believe Scripture teaches clearly both the doctrines of the Trinity AND eternal damnation, Chauncy's theology represents reason trumping revelation, and therefore is not "Christian," even though Protestant Christianity is an element of such creed.)