I'm using the factory ECU grounds, and my battery is in my trunk. I don't trust it 100%, but so far I haven't had any grounding related problems, with the exception of my LCD operation (might be due to bad grounds, but not sure yet), and maybe my P.529 channels died because of poor grounding, but I think it was due to my own negligence connecting the ECU poorly at one point. I haven't felt the need to ground VEMS myself (yet).