I've just picked up a USW-10 relatively cheap on eBay and am planning on fitting it under the dash, probably the passenger side.
Possibly a real novice question, but: where do you recommend powering it from? I'm not planning on immense window-rattling bass, but just making life easier for the door speakers. Is it acceptable to splice it into the wiring adapter (Toyota to ISO) for the radio? Or better to run it from a dedicated fuse in the fuse box? (and if so, which one?)
The generic guides online seem to recommend wiring it straight to the battery's positive terminal but a) that feels like a bodge and b) on our cars, that means running the wiring through the car and through the firewall, which seems like a bit of a faff.
I have a Kenwood sub behind my seat. As the sub power supply had a fuse with less than the cigarette lighter was fused at I used this power as I do not use it for anything else. Been fine for 2 years.
@inigopeteI used piggy back fuses to connect a sat nav and a dash cam.
There is a fuse box in the A pillar on the passenger side , accessible with the door open.
From there it's quite straightforward to get into the car.
You can select a suitable power fuse to piggyback onto.
That was a few years past but still available and some are reviewed here:
https://toproducts.co.uk/fuse-piggyback
Other suppliers are available.
I do not know the size of your sub but I have an amp (for front speakers) and sub under the dash on the driver side, there is a lot of room there compared to passenger side