Parnassus on Wheels. by Christopher Morley

Parnassus on Wheels is Christopher Morley's first novel, and the first of two written from a woman's perspective, the second being The Haunted Bookshop, this book's sequel. Parnassus on Wheels was inspired by a novel by David Grayson (pseudonym of Ray Stannard Baker) called The Friendly Road, and is prefaced by a letter to Grayson from Morley. The word "Parnassus" from the title refers to "Mount Parnassus, " the home of the Muses in Greek mythology.
The protagonist is 39-year-old Helen McGill, who lives on a farm owned by her brother Andrew. The book's Parnassus is a large, horse-drawn van owned by Roger Mifflin, out of which he buys and sells books while traveling around the New England countryside. Mifflin arrives at the McGill farm, looking to sell the business to someone interested in the noble cause of spreading literature to the common man.
Helen is at first turned off by Mr. Mifflin, but decides on a whim that an escape from her dreadful farm-and her insufferable brother Andrew-is just what she needs. She buys the Parnassus, and embarks on exactly the type of adventure she had hoped for.