yeah, just cut the pwr wire and put the fuse in between. The shorter the distance from the battery to the fuse the better. Like this;
pwr wire: [battery]------[fuse]----------------------[amp]
As for the RCA's, I'm not familiar with the interior of Echos and don't know how much room you've got to play with. Generally speaking the RCA wires can be tucked behind the carpet near the passenger foot area. From there, run it underneath the door sill (they just pop off) to the trunk where the amp is.
With respect to the ground wire, 4 ga is better, but 8 should suffice.
If it's not too late, get 4 ga for pwr aswell. It'll save your from having to upgrade later. No biggie if you don't plan on going nuts with the stereo.
Sorry the brief answers - I'm at work. If you run into any probs, I'm sure others will jump into help...they better!
