Does anyone have any ideas or suggestions on how to create a casting outer surface with a consistent wall thickness around a solid body core design.

The outside is the the actual cast part, the core represents a flow path.  Obviously, some feature editing is required to make the outer part 'castable'.  currently,

I am offsetting the faces on the core to the required thickness and add surface features to create and entire outer shell. The outer shell is converted to a solid body, and then

the two bodies, core and shell are combined, with the removal of the core from within the shell.  The time consumin part is developing the shell.  Are there any features or methods that would increase the speed of the entire process?