Sub looks really nice. I was wondering about some sound colouration or mushiness caused by slight flexing of the fibreglass enclosure with sound pressure but the sound deadening, thick covering along with the installed fit should have removed any of that. Once again, really nice job.
I read you mod to the GPS receiver. I have a similar unit and was tracing a Windows USB disconnect- reconnect sound, repeated about 10 times after a minute of PC running time. I realised the GPS battery was draining overnight and the charging current at start-up was affecting the USB extension repeater feeding the GPS. Removed the battery and it’s perfect. I was going to mod for a switch as you had done but at this stage it gets a fix so fast I may just leave the battery out.
Have you had a chance to fire up the sub? looking forward to your thoughts on how it sounds.