A few questions - amp install and door deadening

I have 2 very unrelated situations....

1) I am helping a friend acquire everything he needs to install an amp and sub in his 99 Ranger. He bought a 10' Sony sub (XS-LB10S) and Boss D1200M amplifier = $170 shipped. He is gathering the wires.
Can he use any 4 guage wire to run the power to his battery?
Can he just add an inline fuse just before the battery on that wire?
What size fuse is recommended?

Also, he is going to buy a head unit to replace his factory unit. Does it have to have pre-outs for his amp? If not, what connects the amp to the HU? Its only a mono channel sub and is only going to run his sub.



2) I upgraded the door speakers in my Taco. I did not deaden the door panels (against Marv's recommendation) and regret not doing so. The door panel vibrates. It doesn't make a noise but it feels weird when my knee is resting against it. What is some cheap deadener and where can I get a small kit for just the doors? Cheaper is better...my system isn't all that great anyway.

 

I went with Raammat from Raamaudio. One roll of BXT is enough to do all four doors inside and out (doubled up on the area behind the speaker) and half the back wall behind the seat for the sub. 1 yard of Ensolyte was enough but they have a minimum 2 yard purchase. Plus one can of adhesive (for the ensolyte). ~$150 for all four doors and back wall. There's a Tacomaworld discount as well. Just mention Tacomaworld.

Other than that, I'd look on eBay. I've seen some small door kits on there.

 

If the head unit doesn't have pre-outs, I believe there are some wiring adapters you can get that makes it so you can hook up amps to factory head units & stuff..not sure about non-factory head units w/o pre-outs.