Simple install, want to tune it right. need help

[rbradfordjr]

I know the basics and im trying to learn more and this site has been real informative. My buddy brought me these items and wants me to make a box and hook his system up for him. Not a problem i know the basics on how to wire it so that the sub matches the amps impedance. But i want to design the box perfect and tune it just right, and im new to using WinISD. He has a MTX thunder 300xd with the following specs

• mono subwoofer amplifier
  
• 200 watts RMS x 1 at 4 ohms (300 watts x 1 at 2 ohms)
  
• CEA-2006 compliant
  
• variable low-pass filter (40-200 Hz at 24 dB per octave)
  
• bass boost (0-12 dB at 40 Hz )
  
• subsonic filter (20-50 Hz, 12 dB/octave )
  
• Class D design
  
• speaker- and preamp-level inputs
  
• fuse rating: 30A x 1
  

and a kicker come vr 12" subwoofer 4ohm dvc.

Impedance (OHMS) 2 or 4 DVC Max Rec Amplifier Power (WATTS PEAK/RMS)^* 800/400 Sensitivity (dB 1w/1m) 86.9 Frequency Response (Hz) 25-500 Mounting Depth (IN.,CM) 6 1/4, 15.9 Mounting Cutout (IN.,CM) 11, 27.8 Min Rec Sealed Box Volume (CU. FT., Liters) 1, 28.3 Max Rec Sealed Box Volume (CU. FT., Liters) 4.6, 130 Min Rec Vented Box Volume (CU. Ft., Liters)^** 1.75, 49.6 Max Rec Vented Box Volume (CU. Ft., Liters)^** 2.25, 63.7

Im going to wire it down to 2 ohm to get max out of amp. now my question is when using WinISD how do i know what to set my gain hz and db to in step 1? and what should i tune the vented box to? The gain control on the amp says 5v - 0.25v...idk what that means? ive always tuned by ear. I know the maximum vented volume for the sub is 2.25 cuft. Like i said its just a small simple thing that he picked up from someone for like 50 bucks. I know onec i have the right setting in WinISD it will calculate my length, heighth, and diameter for me and i just have to make sure the vent parameters are within range of the box depth. Hes got a 2001 chevy colbalt hes putting this in. Any help at all would be great! I think this would be a perfect setup for me to learn on before i start my custom build in my own vehicle. Thanks!