It wasn't a ship, it was a nav buoy.

And it required converting it through 3 or 4 formats including 3ds before I got a cob. At that, it was off center, untextured, and didn't turn out the way I'd wanted anyways due to the limitations of the original editor. Trying to use D3Edit to do levels and convert them to FS2 POFs would be more work then making levels in a 3D modeller. Also, D3 levels (the underground/structure parts) are normally designed around the assumption that the player will always be in the level. (In other words, you'd have to make sure the players could not leave the level, the faces are 1 sided facing inwards.)
As for the terrain, simply put that's not really possible.
1. The terrain has a huge number of polys, 65279 if the info I collected when I was working on D3 levels is accurate.
2. The terrain is actually made from a targa file. (Think of it as a really big level you apply a small file to as a bump map.)