Mustang grounding?

I have a 2000 mustang gt. Tonight i will be grounding the amps. My question is, after looking quickly at the exposed metal trunk, it seems that the gas tank takes up most of the floor space and it is looking difficult to find a ground spot. I did however notice a solid steel bar(black) that goes from side to side and is connected to the bottom of the trunk (under the carpet)

Do you think this would be an appropriate ground? Is there a test to see if a ground is a good one or not? I just really dont want to go through that gas tank. And again, should i ground the amps to the same spot with one bolt, or ground them seperately but close?  Thanks again everyone, your help is much appreciated.

That sounds like a torsion bar and it would be spot welded on both sides to the chassis.  It should make a fine ground conductor as long as you remove the paint.  Testing for resistance in the ground return is explained very well in the two featured (sticky) subjects on grounding.  You may not need to go through the process unless you are experiencing problems after the install is done, but a quick test for the bar itself would be to measure resistance from your proposed bare grounding spot to any other bare point on the chassis.  You should find little to no resistance (1/2 ohm would be too much).  It's hard to get that precise unless you know how to use your meter very well, but it can be done.

I like separate grounding points for each wire for the fact that each will be connected directly to chassis instead of stacked on top of another wire connector ring and grounded through it.  Keeping the grounding points very close together limits the possiblity of introducing a ground loop into the mix.