Hi Shazbot, re: "I am trying to do the bottom of that arched shape." maybe it would help if you could show a screenshot pointing to the particular area. Do you mean you're trying to do only some edges around that area that I'm showing above instead of all of them? Sometimes that actually also makes things more difficult for the filleter to handle.

One thing I notice in your geometry is that the bottom of the hood part is not actually a totally flat piece, it's close to being a plane but is instead some kind of sweep or something like that rather than a plane - it generally does help if things that are close to being flat are made from trimmed planes rather than a flat sweep surface or almost-flat in this case.

- Michael