help with box for 18" fully loaded btl

[nej89]

so im in the middle of rebuilding everything in my jeep. im planning on running 4k to my 18. i understand this woofer is only 2k rms, also understand that when u over power a sub u need a smaller box for cone control. i just dont know what box size i need to run that much power to the woofer. and fyi, the 4k im gonna be running is gonna be a clean signal. im gonna have 400ah and a 320 amp alt from mechman with adjustable voltage. i was thinking something around 4 cubes before displacement of sub, 45's and bracing but im not for sure if that is gonna be too big for that much power. so all i need to know really is how big i should design the box.

thanks for the help in advanced, and as soon as i get it all built ill be posting some videos for everyone to see