Replicating and flipping and multiplying a 3D geometry

Given a design which has one instance of a 3D element:

One would replicate this by:

determining a minimum stock size on which the 3D model could be exported from:

first draw a rectangle using ctrl (command on a Mac) corner-to-corner clicking which has its origin at the lower left corner:

copy-paste the geometry which describes the element in question:

Boolean union the two:

OK

mirror horizontally:

and vertically:

and then align with the original geometry:

and draw a rectangle corner-to-corner to get the stock size:

Ok

Export the 3D model as a PNG:

Draw in some geometry to check the thickness of the 3D model:

Revert back to the original file:

Draw in a rectangle which is the size of the previous stock:

Align it with one of the elements which needs the 3D:

Using the rectangle:

Import Image:

Invert

Repeat for each element.