So, I hear that you don't want to use the "titan" game play style for fear of lag. Sounds fine.
I have a suggestion for fixing that:
In some games, the resources required to draw what you can see would be far too big, so those devs simply shunted it to another place.

Quite simply, why not teleport? For example: In some HL2:DM maps, you walk into a "trigger area" and are teleported with no effects or indication, below the level, into your building of choice. One map brought to mind is dm_twoships. The "below-decks" fighting takes place out of sight (When you "noclip" you can go behind the moon and see the interior of the ships) When you "leave" you are teleported back to the moving ships.

This produces VERY little lag, because most of the action takes place on a stationary part of the map, not the moving ships. Essentially you are fighting on a solid map, not a moving object.

I don't know if the BF2142 engine can do this, but it seemed smart to mention it, just in case.

Post here if you don't get it, I'll try to find some screenshots.