John Clellon Holmes’ 1953 beat jazz novel The Horn contains a couple references to Duluth. In the 1988 edition by Thunder’s Mouth Press, the first mention occurs on page 131. I cite it below with a couple paragraphs for context, which make it clear “Duluth” is used synonymously with “some out-of-the-way city on the road.”

The character in this scene is a band leader named Curny. The timeframe is the late 1940s, in New York City.

[…] he was always forming a new band “to hip the public, and incidentally make loot” — a band jerry-built each time out of wild hopes, esoteric arrangements and bone-grinding schedules, which invariably came to no good end after a few months, a few records and a sobering look at the overhead, in some out-of-the-way city on the road.

For all his sartorial affectation of a genteel plantation past, Curny lived almost entirely in glittering future schemes. “This time we’ll lay on the entertainment with an old steam drill,” he would exult to his patient and skeptical wife, Libby. “Every time we get on the stand it’ll be like an act, a camp, a hype. We’ll make the people think we like what we’re doing! Yes sir!” And six months later in Duluth, in the rain, he would pay off the saxes, slip an extra twenty to the trombone (with a habit and two ulcers to support), pack his elegant suits and gaudy neckwear, and catch a sleeper back to New York, to arrive each time, undaunted and optimistic, already full of fresh plans.

…and I’ve come to another one on pp. 160-161, when the character Metro is hopping freight trains, living that life and encountering hobo myths:

It would always be the first dewy awakening in sweet spring fields moist with new-turned loam; the great mist-choked bends of continental rivers, tidal, tremendous, with their half-sunk cargoes of orange crates and contraceptives and wishful, stoppered bottles, containing matches for imagined castaways, that had been consigned to the muddy current somewhere up in mythic Minnesota by dreamy farm boys, safer than yourself. It would be the long laze of murmurous summer evenings by a hobo fire […] “That Evanston mission, no — you got to stand up for Jesus just to get a crummy day-old bun” […] It would be stories of the mission, some said in Duluth, some Rock Island, some (with veteran eyes) insisted that they moved it place to place, Loosfer’s Mission, where they made the stew of mangled kids who fell between the couplings, and kept you overnight in lightless cells until you hollered “Yes,” and shipped you in a phantom redball to a bayou chain gang, to lay track they tore up every night.