Well, there are a couple of good plugins for working with terrain in general:
Terrain reshaper to give your terrain a nicer, even subdivision: http://forums.sketchucation.com/viewtopic.php?t=11320
Point merger (in case your terrains do not precisely match): http://forums.sketchucation.com/viewtopic.php?t=19838
Curviloft to stitching pieces in case they do not match at all: http://forums.sketchucation.com/viewtopic.php?t=28586
Vertex Tools for super easy manipulation of meshes (this is a commercial one but very useful): http://forums.sketchucation.com/viewtopic.php?t=29636
and probably some more