A ship-based printing press, plying trade as mobile printers, is the background for Vernor Vinge's Tatja Grimm series. I need to dig it out to provide quotes, but a review on Goodreads yields:
the planet Tu on which the book takes place is a metal-poor world where humanity has had to adapt using ceramics and wood for everything. The first half of the book is set on a giant traveling publishing barge that sails the oceans of the planet and sells, among other things, a speculative fiction pulp mag called Fantasie.
(emphasis mine)
The original publication was as a short story "Grimm's Story" in Orbit 4 (1968), so if you're recalling a short story that may be it. (There was also another short set on the world published in Analog in 1986. Both were combined into the later novel-length fix-up Tatja Grimm's World.)
From the introduction to the story in Orbit 4:
The planet called Tu is a world of oceans and scattered archipelagoes. Tu has a sister planet, Seraph, hanging eternally fixed in her sky—a more tantalizing goal for space flight than our Moon. But Tu’s thousand-year-old civilization has almost no metals. With a wood-glass-and-plastics technology, the island people have hydrofoils, telescopes, even photography, but no heavier-than-air craft, let alone spacecraft: they can only look up and wonder.
And from Tatja Grimm's World:
“Not like this one. Ivam Alecque knows astronomers at Krinsarque who are hanging spectro gear on telescopes. They’ve drawn line spectra for lots of stars. The ones with color and absolute magnitude similar to our sun show
incredibly intense lines for iron and copper and the other metals. This is the first time in history anyone has had direct insight about how things must be on planets of other stars. Houses built of iron are actually possible there.”
Ascuasenya was silent for a moment. The idea was neat; in fact, it was kind of scary. Finally she said, “We’re all alone in being so ‘metal poor?’”
“Yes! At least among the sun-like stars these guys have looked at.”
About the publishing barge:
In the first place, the Tarulle Publishing Barge wasn’t due in the Krirsarque area for another three days. Svir had been very upset to learn
that his ship would stay a day ahead of the Tarulle fleet as the publishing company sailed slowly east along the Chainpearl Archipelagate. He wouldn’t receive the latest copies of Fantasie—all two years’ worth—until he reached Bayfast in Crownesse. In the second place, the Tarulle
Barge rarely landed at minor places like Krirsarque. The Barge dispatched its hydrofoil sailing boats for such contacts. These boats delivered the company’s publications, and took aboard supplies and manuscripts.
And a bit about the barge itself:
The Tarulle Barge was especially impressive by day. Over the centuries, it had grown helter-skelter. New barge platforms had been added and built upon—then built over again, until the mass resembled nothing so much as a man-made mountain of terraces, cupolas, and cranes. The top offices and printshops were of spun glass —the most modern construction material. The bottommost members of the Barge were moldering timbers three hundred years old. From the top of the mainmast to the bottom of the lowest hold was almost three hundred feet.
(Quotes from "Grimm's Story" since that's the first short story version.)
