Creating a Tin file from Model

I have a rather large model made up of several files and I need to create a tin every now and then to do some detailing in the plans. My current method is to select all the surface shapes that I need and create a terrain out them, then export that terrain to a tin file. I even create an Item Set out of the selected surfaces so that I can come back and create the tin again, or add to it if I need to. I generally delete this tin after I export it because I dont need to keep that element in the file any longer, so the Item Set helps me quickly recreate that tin file. 

Im just wondering if anyone has a better method, or if there is more of an automated utility to handle this. This isnt a big deal for one roadway corridor, but in my case, I have a road, two ramps, ponds, and canals all coming into this same area, so I have separate model DGN's for each and lots of surfaces that need to be added to this tin.