Im going off to work on it now, heres what im going to do, im going to export the terrain to a 3ds file and then import it into max. then i merge the tunnels into the terrain and i line up the vertexes and delete the faces inside the tunnel, do some texturing. Get rid of the terrian in nolimits and import the one with the tunnel in it. Thanks to torch511 for telling me this a while ago.
Should be done in a while.