Where is a good spot to ground your amp? Im mounting it to the box

 

What box? Speaker/sub box in the back? Any place you find a stud or bolt with bare metal under it. Pull up various pieces of carpet. There are studs everywhere. There are GREAT ones under the center console and in the driver and passenger footwells. At the very back just inside the tub from the tailgate should be a D-Rings tie down. That would work if your amp is all the way back there.

 

What guage wire should i use to power an alpine pdx 1.1000 ?

 

The manual should state this. I believe Alpine requires a 6 gauge minimum, but they recommend 4.