I found I can only add one extra mesh to the background in addition to the planet, and having things in the map area (or close to it) might be difficult. The tiny Phobos and Deimos meshes look huge in the background, which wouldn’t suit for drydocks…
Ignored, more testing is required, I got side-tracked with shared texture fixes last night
I also think Salvage is added as part of the game rule, not the map, but there’s maps with big hunks of debris in it so I’ll have a look at the defaults there for a clue!
I ended up just copying the *.ship file of a piece of wreckage from one of the default maps. Something in there is flagging it for the game to load the HOD, don’t know what though. But I got my map objects to show! Yay