Even though I am kind of far from the end of transcribing and digitizing the letters, I occasionally look at some libraries with collections of war materials and letters. I don’t want the physical letters to be a burden to any family member, nor remain hidden in a personal collection. When I’m done, I would rather let them go to a permanent library collection with other letters of their kind.
One interesting place is The Center for American War Letters at Chapman University in California. I’m not sure why they specify that it is a repository of “previously unpublished” letters or if that would disqualify mine after I publish them, but it is one place I am considering. I’m sure some of their scholars want to write their own books that include letters; maybe that’s why they want unpublished letters. Interestingly, this university was founded by members of the Christian Church (Disciples of Christ), the denomination in which I was raised.
There are also library collections that focus on letters from specific wars, such as the Civil War or one of the World Wars. Since my letters span two wars, I should probably look for a more comprehensive collection. Probably you can donate such letters to just about any library, but I will have to see how publication affects working with any library.