Consider this book to be a valuable knowledge resource, or a companion for that matter, throughout your van build journey. I consider it to be a narrative that one should follow during the build, and that one can always turn back to.
What I think that this book is not, is not a deep knowledge source for the various build areas (gas,water,electricity systems, insulation, etc). For that, I recommend the reader to read specific books on those topics, or hire professionals.