I have not come across many marathon reads. Ulysses by James Joyce seems to attract multiple reads a year, but there are many other location specific works which would be great for this (and if they could be streamed online that helps people who can't be there). Last year there was a reading of the Illiad, which is still available for a few more months of listening.
There are, no doubt, a lot of other marathon reads out there, which I have not included, but think of it as a way to have people consider local history, and local stories. The reading may be of works of fiction, such as Moby-Dick, or of non-fiction. It can be a way to connect people together. Consider it as part of your library programming.
I can find find the history, local studies and readers advisory elements of interest but I am against any current whaling.