I usually write about Universalist polity, but some chat a few weeks ago about "Beyond Congregations" reminded me about the English "Unitarian van mission" of more than a century ago, and interest that stirred up here in the United States.
I've found references as far back as 1908, with its evident zenith in the 1910s. According to Georges Salim Kukhi, himself a London Unitarian preacher in 1919, there was more than one van, indeed, four that roved Britain. The vans have not only a pulpit, but sleeping quarters and room for print material. They were fitted with technically-advanced acetylene lamps!
Preachers, sometimes lay preachers, would address the crowds from the van; sometimes they'd be harangued. But it seems there was also a desire for information:
The Unitarian Van Mission in England allows its out of doors audiences to ask questions and finds frequent anxiety for information concerning the talking serpent in the Garden of Eden the veracity of Balaam's ass the truth of the whale and Jonah incident and other Old Testament marvels.
They would also distribute publications.
I've not been able to find evidence of a Unitarian van in the United States, though there was a stated desire and a bit of embarrassment that that the gung-ho Americans didn't do it first! (In fact, there was something called a van mission in Kansas in 1896. That's something to research.)