Good hint! Any idea on max diameter?
Many thanks,
From feeling up behind the dash about 50mm is free between the frame and the edge of the glove box, but to be certain you need to take the dash off. On the drivers side 50mm is fine, as Jays showed when he fitted a clock.
You will have to take the dash off to fit the speakers and to get at the side panels and do the wiring and fit the power amp. Again, the side panels are not that rigid, I think I'd replace them with 3mm aluminium sheet, re-upholstered and with damping material on the inside would help. The idea is that they cannot vibrate. The dash is fine!
Thinking about fitting the head unit it might be a good idea to modify the glove box so it fits in there and is totally hidden when not in use. The standard position is worse than difficult to get at.
I'm still very concerned that doing a proper job might sound great but make it a thief magnet.