I didn't think I'd ever see a book (and it looks like a nice one) about this obscure aircraft.
A little known fact is that the Douglas B-18 Bolo was America's most numerous front line bomber at the time of Pearl Harbor.
The full title is "Douglas B-18 Bolo - The Ultimate Look: from Drawing Board to U-Boat Hunter" by William Wolf (ISBN 978-0-7643-2581-6) USD $59.95 (retail).

Chapters:

1. Donald Douglas, the DC Airliners, and the B-18
   
2. Prewar American Bomber Development and Procurement Policies
   
3. Development of the B-18 DC Bomber
   
4. The B-18: Description
   
5. The B-18 in the Continental US: 1937 to the War's End
   
6. The B-18 in Hawaii
   
7. The B-18 in the Philippines
   
8. The B-18 in Alaska
   
9. Anti-Submarine Warfare: The B-18 Finds its Niche
   
10. Canadian and Foreign B-18s
    
11. B-23 Dragon: B-18 Upgrade
    
12. Disposition and Obscurity
    

The B-18 description chapter has interior shots of a restored B-18.