Hi David, yeah that's a fairly difficult shape because it's not quite symmetrical so that won't quite work with Revolve.

A 2 rail sweep might be a good approach though - see the attached 3DM file.

To construct this, I drew one long curve using Draw curve > Freeform, tracing the background image shape:



Then in order to use that curve as the side rails in a 2 rail sweep you have to cut it into half, to do that select it and run the Edit > Trim command, and push the "Add trim points" button inside of Trim and click on the spot at the top of the curve to cut it. Then when you finish the Trim command it will cut that one long smooth curve into 2 pieces.

Then I drew in an ellipse like this:




Then select the ellipse, and run Construct > Sweep, then at the next prompt select the 2 side rails and it will generate a result like this (in the file):




Then probably the little side nodule would be good to build as a separate piece that is then booleaned together with this main body piece. The image you have here is very low resolution, it's kind of hard to see what that nodule is shaped like. Do you possibly have a higher resolution photo that gives some better detail on that part?

If it's more symmetrical it may work to do a revolve to make a kind of donut like form, then boolean that with the main body and then do a fillet to smooth out the connection.

- Michael