on the lid? absolutely! depending on the dimensions of your amp it should fit without issue.
but mounting the amp on top would not result in a stealth install... it depends what you're after i guess.
my amps are currently screwed into an old wooden drawer which is inverted and bolted to where the spare tyre would be mounted. it's a temporary thing until i extend the wires for the Bose amp and find a suitable hidden home for both.
you can easily gain 30-40% more cargo space by removing the spare tyre and all the foam. but you run the risk of being stranded - mobility kits are futile for huge punctures so the other option is to fit runflat tyres. the lucky thing is the F10 BMW 5 series can be outfitted with identical sized tyres to our Z (assuming stock Rays 19") so runflats in our size do exist. Only problem is you're limited in choice and the tyres are designed for heavier cars, thus may not offer as much grip as the better non runflats like PSS.
anyway, that's for another topic
