Another area that looks like a problematic structure is this area here:



Those 3 surfaces look like they're flat to one another but when I removed them and tried to create one single large plane (which is better for filleting), it would not build it there, which means that you've likely got another one of those very shallow crease type shapes in that area. That's going to make it difficult for any fillet to work that has to go through that zone.

- Michael