Stock amplifier is only 25 watts or so at best.
Most mono amps for driving subwoofers are huge power.
Most efficient and smallest physical size will be D Class amps.
Rockford Fosgate D Class mono amplifier
Has high level input, gain control and X-over.
300 watts at 4 ohms
Size: 8.5"x7.5"x2" thick
https://www.amazon.com/dp/B00BF6HYDEAnother good choice would be a mini D Class amp like Clarion.
200 watts at 4 ohms
https://www.crutchfield.com.../Clarion-XC2110.htmlManual:
https://www.clarion.com/us/...C2110_manual_EN_.pdf.------------------
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3.4L Supercharged 87 GT and Super Duty 4 Indy #163[This message has been edited by fierosound (edited 04-25-2020).]