Help with Amp Ground in Trunk

[Meldav86]

So i'm installing one amp in the trunk to power the sub, i have the power routed from the battery, all fuses are good, and the remote wire connected but the amp just won't power on. I'm almost sure it's just a bad ground. I used the bottom right bolt in the picture. I used a dremel to expose some metal. I don't know if it has anything to do with it but the bolt screws into a plastic piece. If anyone has any insight to trunk grounds please help. I think what i will try is maybe one of the seat bolts, but what kind of socket does it require as it is shaped different. Do i need torx sockets?