I'm thinking that the wintergarden would be associated with the turms. Myself, I've not done enough noodling in OM, nor am I familiar enough with all of the Uboat variations, so which version are you referring to there THEBERBSTER, the IXC? Are there guns on the one you are referring to, but it's just an inappropriate flak decking configuration for the boat? I had always referred to "wintergarden" as the "porches", fore and aft, for the mounting of flak guns, but I know some refer specifically to the Type VII U-flak boat version as "wintergarden"...
2nd Flotilla at uboat dot net
https://uboat.net/flotillas/2flo.htm