i have a design for a custom box. Buck at High Output Enclosures made it. its for a mid to high powered 15 in a medium to large ext cab pickup. example- Dodge Ram 1500, Chevy K1500 or likeness can be used in Jeep Wrangler also. port is tuned at 33Hz. box was originally designed for a DC audio XL but can work with any sub over 1500 peak watts. ill sell the design for $20. i paid $30 for it.