I have been working on this part for a good amount of time and I just keep running into problems. One problem i am facing is no matter what I do I can not get a feature (this feature is blue in the "end" file and the surface that it comes from is blue in the "start" file) to extrude as a solid to the inside surface of the shell mock up (the shell mock up is the red feature). I can extrude it as a surface then thicken (this part is blue) but after I circular pattern the feature I cannot shell the combined group of features ( the features that need to be shelled are every color except red and the face that needs to be removed is yellow). The next problem is I need to delete the shell mock up, red part, but when I do that I am going to loose the extrude to surface feature and I don't know how to keep it. I have included two files the one labeled "end" is what I need the part to look like in the end (except the fact that it is not shelled to .2 in) which includes the the thickened surface in blue, the circular patter,green, and a magenta feature. The file named "start" is the where i started at and is included so it may be easier for you to help me. Any help on this is greatly appreciated and will help me not go insane.
If you want to know what the part is, it is a impeller pump shell for a submarine
First: your initial sketches are not constrained-- very poor practice and will lead to trouble at some point.
I'm not going to try to figure out the whole thing, because there's a lot I don't understand about your design. But if you want to extrude to the inner surface of the elliptical outer shell, but not retain the surface as part of your solid, then here is my suggestion: edit Extrusion3 and change it from Join to New Solid. Then you can use the Delete Face tool to delete the outer faces of the outside shell, leaving just the one surface (the red one). This surface can be made invisible once you're done with it, and won't appear on your drawing.
I think the problem you're having with the shell is just a complex geometry problem. The loft feature is just not shellable-- at least I can't quite picture what a uniform wall thickness would look like in this case.
I think lots of folks here would like to tackle your problem, but you'll have to provide an image or drawing of what you're trying to achieve. I can't tell from your model, anyway.