For 2 complex shapes or surfaces I need to determine the volume enclosed between the 2.
1. Use the loft surface tool create a surface between the 2 surfaces of interest. Enable the keep profiles options for subsequent steps
2. Use the Stitch Surfaces Tool to create a closed volume of the 2 initial surfaces and the created surface from Step 1.
3. Determine the Volume using either the Measure Volume tool or check the properties Dialog
Surface Between Volume Calculated (Forum)
Loft Surface
Stitch Mesh