The true test of your seat bolt ground is to measure the voltage at the amplifier when you hit the key. It is possible to have a connection that looks good when checking resistance because it has no load. A situation like this could deliver adequate average power out of the amp, but peak power would be lower than rated.
Or you can say that it works ok so that means that it's good. If you're not worried about it being the best that it can be, then what it is, is good enough. I am not trying to be snarky, I am just letting you know how I look at it. You can run your stuff however you want, we will always be here to help.
Chris