Extrude surface in both directions

What is the best way to extrude a surface in both normal directions to get a closed B-rep with a specific thickness? If I do the two extrusions separately and try and merge them using Solid Union, I often run into merging/tolerance errors since they only intersect at the original surface.

Extrude in full “normal” direction, then move half the distance in the opposite direction with expression “-x/2” on the Move ‘T’ input.

That’s a great technique, thanks!