My tunnels always had Tunnel Liners as deep into the tunnel as was viewable from outside. Where possible, I made the liner's roof removable to be able to retrieve; or, repair things needing such. My liners where made to look like a bore through rock; or, had wood support beams attempting to make it look realistic. All of my tunnels used Chooch; or, some other manufacturers Tunnel Portals, mostly wood structures, or stone. On some, the scenery base used a cut to get to the bore. Simply put, I tried to make the area look as realistic as I could.