Sorry I didn't reply earlier. We have family visiting from out of town and I haven't had time to mess with this little project.
Basically this is a sub woofer design I'm making based on a studio monitor. The studio monitor has a special type of flare to the port that helps to eliminate port turbulence (see photos).


I'm designing this because there is a YouTuber that has a competition (for fun, no prizes) where he is taking different 12" sub woofer design submissions and 3D printing them on a 1/6th scale and measuring the output (also scaled) and comparing the way different designs perform.
I wanted to implement this studio monitor design as a sub woofer and submit it to see how it performs. I have made another attempt trying to use two forms but I cant figure out how to fill it in (See Photo, Don't laugh).

I want to ensure that it prints out properly and doesn't have a void and that all of it is sealed up nicely. I know I'm probably not doing this right. I'm still very new to Fusion 360. I have used Blender and Sketchup for making 3D models before but not for 3D printing. I would like to learn the proper way to do this as I plan on trying other projects with Fusion in the future.
Thank you in advance to anyone that can help!