I'll be putting in new Infinity componant and was wondering where is the best location for the crossover??

 

Where ever you can fit them that work for you.
Under the seats, center console, on the back wall, under the dash, behind the kick panel. Tons of places.

In my 99 I had them mounted on the firewall, under the dash.
Hell, I just had short nails pressed into some thick black mat stuff on firewall...3 years and I never had one fall off or move.

 

In my supercrew, is there an advantage to mounting them behind the seat with the amps or should I leave them in the door arm rest?

 

Advantage?? Not really.

Only advantage I could see is that you have everything mounted together on the back wall then...which really isnt a big deal at all unless you **** about something like that.

It would just be a PITA to change them...would have to run more speaker wire, etc. Your not gaining anything by moving them if they are working where you have them now and your happy with it.

 

I have mine mounted in the door