From bottom to top:
1. model with 2 topologically matching meshes – outer (by extruding inner and deleteing all but the original faces) | inner

2. Sandwich structure rebuilt by iterating edges on both mesh and join.
By rebuilding the structure inbetween, the inner mesh can be manipulated separately from the outer mesh (using maya scuplt geometry tools/soft move) giving different thickness/sizes at different parts on the final model – as long as the number of edges, faces and vertices are the same.

3. Alternative sandwich structure rebuilt by iterating faces on both mesh and join, using center point on each face on the outer mesh. Rebuild outermesh using each face center point. (same as previous post titled thickness mesh frame)