Having come from bigger cars with more space to hide stuff (DC5, Audi S4, Civic FD2), the
Cupra has been a bit more of a challenge. Still, with some careful placement and a lot of thought, we've managed to shoehorn all my gear from the Civic:
Kenwood DNX8220, TV tuner and rev camera (ok, the camera is overkill but already had it from the FD2, so why not?)
Rainbow SLC 3-way components, plus an extra pair of 17cm midbass in the front doors
False floor in the boot covering a pair of Audison LRX amps (4.5 and 1.1k)
Hertx HX250D in a removable box - takes up a bit of boot space but I don't often carry that much luggage, so for the rare times I do it's easier just to lift the box out completely.
I'll get some pics up once it's all finished, I'm still waiting on the last couple of bits for the door builds which should be in by the end of the week.