Good morning @[theotherone].
You can find some answers on the following thread on page 3:
http://www.bmwhaus.ie/vbulletin/show...ound-Deadening

I'm sure Mike(Germaniks) will be able to sort you out

You can also ask other people what they did with their builds like claudio who recently did this on his convertible

Other alternatives depending on budget could be B&Q.
I know a member who did the soundproofing of his car with the following:
http://www.diy.com/departments/knauf...m/26877_BQ.prd
I would not know and can't remember how he managed to fix it to the car though?

Last not least ordering on line like you did. From what I remeber in the good old days the best would be Dynamat. There would be this Trunk kit they do which costs 80 pounds, does 20 sq. feet and seems pretty good:
http://www.deadening.co.uk/products/...k-kit-dyn10945

As you can see you have quite a few alternatives. For sure sound deadening is much better than nothing at all as it will keep the sound in the car rather than it being dispersed in the panels