Stereo. amps. & sub questions

[rauto13]

I just got a 12" sub installed behind the seat, sounds good, I think I have already pissed off the neighbors. I have a couple questions though.

The rear panel of the truck now vibrates badly whenever the sub hits. Will Dynamat or something similar stop this vibration? It is pretty annoying and the vibration sounds really bad outside the truck.

I put in a Jensen amp that I had laying around. The amp is 2/3/4 channel. I have put the amp in three channel mode and bridged the outputs to one four ohm sub and did not hook up anything to the other two channels. Will this hurt the amp running bridged into one sub, with nothing on the front channels on the amp?

I looked up the instruction manual online and the amp is meant to be bridged and can run four seperate channels, two channels with the rear channels bridged (three channels), or front & rear channels bridged into two speakers (two channels). I am thinking it is okay to run just one channel off the rear bridged outputs, but don't want to burn it up.

Does anyone know how well a passive radiator setup with one 12" sub works? I need as much room behind the drivers seat as possible, hence only one sub behind the passenger seat. I thought about using the Blaupunkt overdrive subs and cutting my box down, but they are not available any more. Too bad, only three inches deep mounting depth.

Anyone else know of any very thin mount 12" subs, say 4 inches mount depth or less?

Thanks for the help.

ps. Anyone got a couple of 12" Blaupunkt overdrives ya don't need anymore?