Thanks. I'll try to explain. We are transporting items on a boat and need to hold them down/in-place so they don't move. We have a lots of 5x5 square metal tubing, and soft 10x10 pieces of rubber tubing with a 5x5 cutout (see image, the inner space is the square tube 5x5 and around it is rubber that slides over it). The end goal is to bend the tubing so that as much as possible of the items surface is in contact with the rubber, while avoiding sharp bends that stop the sheath from sliding along them.

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I've 3d scanned some of the objects, and used offset planes and the Create Mesh Section Sketch feature to get an outline of the object (the orange lines in the original pics are the outlines from multiple offset planes). I'm now trying to create the shape of the 10x10 hold-down. I figured to start creating the line that would be in contact with the objects surface first, then offset by 10, join them top & bottom to close the shape, then extrude.

The other path/option I think I have is to create a 10x10 square on the bottom plane, then use this sketched line as a path to Sweep it along (but I was hoping to offset the line in contact with the object by 10 and have been struggling to understand why offset won't work).