Hasta La Motion!

Firstly, apologies, I can’t post any images so I’ll describe as best as I can.

So, a guy is standing outside tunnel entrance kind of thing and then he walks into it with the camera following. I need to replace the walls inside the tunnel.

I can get a reasonable2d track but only up to about halfway. What happens then is that all my tracking references go off the screen and I can’t offset as he is pretty much in the tunnel by then and I can’t get anything to track, it’s almost pitch black.

I’m trying to do a 3d solve but I don’t have much experience with this. I’m just trying to use the wall as a track (as when it tracks the guy the camera bounces up and down with his walking movements) but then I get pretty much the same problem with the darkness (although the start is much smoother). Is there any way to extend the camera move, like a predict track sort of thing?

Any tips on how to solve the camera better? I know this is kind of vague but any suggestions would be really good.