For joining lines to 3dpolys, I suggest this code :
http://www.cadtutor.net/forum/showthread.php?98911-convert-lines-to-3d-polylines&p=#7And in attachment there is your DWG with my intervention...
1st step is to break lines to intersecting points...
2nd step is to join every each continuous segment to 3dpoly using my routine I pointed in the link (or if you find it better - just use JOIN command)
3rd step is to check each intersecting vertex if when stretched and gripped all connecting 3dpolys weather vertex is common - you should see all connecting segments move along with stretching vertex
4th step is to use EDGESURF command on 4 touching edges to form surfaces...
HTH., M.R.
Regards