Cura - Closing off top and bottom of Open item

SO I have a part that is essentially a tube with compound curves. While one end is open it does have a large flange so I made that the print surface.

However, Cura either wants to close both ends off completely or not at all. Here you can see the original drawing, note that you can see all the way through.

When I get it into Cura - in Ghost view you can see the flange at the bottom

So with Bottom and top >0 I get a solid closure over both open ends even though the drawing has no top at all or solid bottom

Ok fair enough, set top and bottom to 0 so now when I show the layers I do not get the flange that IS in the drawing. So, I either get a roof that can not be printed and a solid layer on the bottom where it should be just a flange OR I get a no flange at all on the bottom.

So what dumb noob mistake am I making! :slight_smile:

I am not an expert with Cura but I do a fair amount of CAD work.
In your second picture it looks like your model is just a single surface shell.
I would think you need to complete the model so that it includes the outside, inside and end surfaces, and defines the wall thickness you want. This would all be done in your CAD program before you even get to Cura.
With thinish walls I try to always make the thickness a multiple of the nozzle diameter. Seems to be easier for the slicer to deal with.