Here's a couple of links that you may find interesting...
http://en.wikipedia.org/wiki/Type_II_U-boat (click the CV-707 link and then the pictures link to get a bit of an idea)
http://www.uboataces.com/uboat-type-ii.shtml
As you've found, there's just not too much ink dedicated to the ol' coastal boat. I wonder though if there is one of those Osprey-type publications on it?