Terrain net object

I'm trying to modify the terrain so that it would be destructible, and I'm still trying to figure out the whole engine in the process.

I'm just wondering why in earth the TerrainBlock::packUpdate() packs the empty square RLE:s? Is this information something that's likely to change while playing, because as I see it, the empty squares are created in the editor, and that's that.

Also more on the general note, in what order are the networking components set up? As I see it, unpackUpdate() is called first, then onAdd(); is it so? (btw, what is the return value for the packUpdate() for?)

So if I create a destructible terrain (class DestructibleTerrainBlock : public TerrainBlock), I would send the terrain in packUpdate() and then all terrain modification event as separate NetEvents?

Thanks!