Having fit a new tracker on my bus recently it struck me how few options there are in a Bay to conceal the device/aerial (which granted are much smaller than they used to be) whilst still delivering a "view" of the satellites that isn't obscured by metal shielding. Not easy. The only hard wiring needed is a simple 12v supply to keep the battery topped-up. Not essential, but will make it a fit and forget install.
Also eBay is littered with £10 jammers that claim to deprive any tracker of its gps signal. I'm not sure how effective they are (not being a gangster) and I think most systems will use cellular tracking info if the gps is lost. That's less accurate, but a decent start.
Overall the device I chose cost about £70 subscription-free and does a much better job imho than the expensive RAC tracker I had on the bus before... And the insurance premium no different.