Are there any books you would recommend re: object relations theory and its use in treatment? I'm particularly interested in how it is used with people with PTSD.
I would say that most object relations literature implicitly contains a theory of treatment. Object relations theorists tend to emphasize the use of transference/countertransference and enactment in clinical practice. I'm not sure if I know of any books that are more "clinical" than they are "theoretical" but here are some books that helped me get acquainted with object relations theory and helped me think about my own clinical work:
Object Relations in Psychoanalytic Theory by Greenberg and Mitchell
Essential Papers on Object Relations Ed. by Peter Buckley
Object Relations theory and Clinical Psychoanalysis by Otto Kernberg
(I also like his primer of transference focused psychotherapy)
As for books dealing specifically with trauma:
Either of Philip Bromberg's two books
or
Treating the Adult Survivor of Sexual Abuse by Davies and Frawley
(I especially recommend this one!)
Most everything by Masterson and Kernberg should be at least reviewed to get a fuller picture of how Object Relations came to be, though their writings are far from 'how to' readings.
"Object Relations in Severe Trauma: Psychotherapy of the Sexually Abused Child" by Stephen Prior is also a good read, though, as the title indicates, it is somewhat narrowly focused on the sexual trauma of children.