Here’s an idea for you.
My son was throwing out his gaming chair. It runs off a 12v transformer so my mind started working overtime. 12v, stereo speakers, subwoofer in the seat, this has potential.
Even if I was buying this chair purely for the sound system, I’d still have a chair once I’d ripped the sound system out.
I had to reduce the subwoofer by 37mm to fit in the boot, but this wasn’t too difficult with a sharp saw and some wood glue.
The stereo speakers were a good fit for the existing housings in the roof.
After also securing the amplifier in the speaker housing, I fixed the control panel for easy access. The small box tucked into the roof is a Bluetooth receiver copied from elsewhere on this site. You will note that this has controls for the bass and volume (I didn’t think the vibration unit was worth transferring across).
I can now either Bluetooth internet radio or stream tunes from my mobile phone, all for less than £120 (well less than £30 when you think that I got the chair for nothing).
You will need a cigarette lighter splitter, an extension cable, some speaker cable, a Bluetooth receiver and a cigarette lighter plug to complete the installation.