I don't know much about the U-Boat ports but I do have some very good sources in pdf format for anyone who wants to try modeling them.
IMO there are many additional shoreline structures needed make the coasts of SH3 seem more "alive":
-Different styles of lighthouse
-Lifeboat stations & lifeboat ramps
-Piers
-Different-sized ports, such as fishing villages & small industrial wharves
-More types of shipwreck
-Oil derricks
You get the idea.
I have actually started researching the Chain Home sites and I kitbashed a crude British radar tower from one of the SH3 cranes in the harbor kit. Unfortunately, with all the work on the Merchant Fleet Mod I have not had time to get very much done.