Humm, what cab? Crew cab box? The Sundown Motors are way too big for that box.
Reg Cab? Then yea Sundown subs will fit.
I have both Fox Boxes. SunDowns in my Reg Cab with many watt's. Hits really hard.
The other FOX box I have is the one that goes under the seat in Crew or Quad Cab's. 12" Kicker Comp's Subs. Very hard hitting, deep bass. Them black boys know this old white man is coming, 40 blocks away. In ANY of my cars or trucks.