The Dayton was suggested to you because your originally statement regarding your budget:I went from being suggested the Dayton 15" HF to the Mach 5 IXL 18.2.2. If I wouldn't have asked the questions, I would have ordered the Dayton.
You changed your mind and different subs were recommended. Moving on.......My max budget is $425, but I would like to keep it below $400, if possible.
Your box plans look fine.