Based on the type of OER, it may be more appropriate to add your materials to YouTube, Vimeo, Flickr or other websites for video/audio. You do not have to limit yourself to one platform
Adaption Guide (BCcampus) is a practical guide about how to customize — or adapt — an open textbook so that it better fits your needs in the classroom and elsewhere. See their Five rules of textbook development
Open Education Self-Publishing Guide (BCcampus) is a reference for individuals or groups wanting to write and self-publish an open textbook. This guide provides details on the preparation, planning, writing, publication, and maintenance of an open textbook.
Modifying an Open Textbook: What You Need to Know (Open Textbook Network) is a five-step guide for academics who want to modify an open textbook. Step-by-step instructions for importing and editing common open textbook file and platform types are included.
Authoring Open Textbooks (Open Textbook Network) Content includes a checklist for getting started, publishing program case studies, textbook organization and elements, writing resources and an overview of useful tools.
Creating and Modifying Open Educational Resources is a chapter-by-chapter informational tutorial for academics interested in creating or adapting open educational resources.