I'm hitting a brick wall on this right now. I just bought my first avalanche, an 05 Z71 with many nice options, and I love it. I bought a box with two 10s that "fit" under the rear seat. Now realizing, and reading here, that I should have gotten a single sided box. Would have been easier to remove to use the midgate, and would have allowed me to choose the sub I wanted. This one came with two subs of unknown quality, 250 watts RMS each.
I don't want to cut up the truck, at all, and due to the number of adapters needed to get what I want in the truck and integrate steering wheel controls and keep rear seat audio working correctly, and considering the 235k miles it has, I'm just going to ride with the stock radio and add bluetooth the gangster way. I just soldered together a PAC RCA out (for my sub amp) and a bluetooth receiver to the harness that comes with the PAC, got it all working, then realized I have nowhere to put the amp and therefore can't run the RCAs and put my dash back together. I used the RCA out from the bluetooth receiver and connected them to the analog left/right signals that are used by the XM radio (or used to be). Now I can have everything I wanted (bluetooth, output for subs, retained accessory power signal for subs and bluetooth, steering wheel controls, using factory amps, retaining rear seat audio) for the low cost of $64 and an hour of time.
All this to say.... the link for the modification to the under seat box doesn't work anymore, and the more I think about it, the more I'm considering mounting this amp in the cargo bins of the bed of the truck. Someone please save my sanity and show me how to mod this box, or post some photos of other noninvasive installations. I'm using an Alpine MRP M500, so nothing huge.