I have the same setup as you, when I got my tank it came with a 7 gal
acrylic sump. I wanted a fug but space was a issue as I'm sure you know. This Is what I came up with and it works well In the small space & I've got about everything I need in there. The only thing I would have done different would to have put my skimmer before my fug instead of after. But other than some green foam I have seen no issue.