I was wondering if anyone had any ideas for filling a 3d Train cake??

Are you starting out with a basic square/rectangle?

If so, tort and fill first and THEN carve. 

Freezing for a short period to firm it all up will help.

Suzanne x

I was trying to find a way to fill it after it is already baked in the 3d pan itself. I might just have to shape my own and fill it that way instead. I bought the 3d cake pan from wilton and its great but there is no way to cut it and fill it unfortunately.

AI just bake it then slice it up, dam and fill, stack it back up and go!

I just made this cake a couple of weeks ago by stacking rectangles and carving.  I was concerned that the round part wouldn't hold up, but I had no problems at all. 

I cut and filled the Train pan from Wilton a few weeks ago, I didn't have any problems...just watch where your cutting.  Good Luck!