I am posting this here to share a support email I sent to DotSoft.
I had a problem with:
> Manage surfaces
> Points on a grid
> Drape
There was no option to select a surface even though I just created both TIN and GRID surfaces.
The response from DotSoft was:
Currently surfaces reside in files and if those surface definitions reside in the same folder as the drawing, or in the search path, then they show up in Surface tools.
We have been experimenting with ways to store surfaces in the drawing (like Civil3D can) but we're still not sure we want to. The speed of I/O and the file size growth are concerns.