Years ago I used to work in car audio. You can do crazy stuff with MDF and bog. However I had keeping it standard in mind.
I wonder if you can fit the entire D2 door card into a D1? If you did all four it would look kind of factory.
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You won't get the DII door cards to fit a DI door but you can get much better speakers to fit the DI than the standard 100mm ones.
I used some MDF and a Dremel tool to make these spacers and also used the up-market Disco pillar trims to mount some after market tweeters. The standard tweeters sounded okay but the Rockford ones are much better.
Edited. The system won't allow me to apload my pictures today! Will get back later.
See here for a similar thread I started some time ago. http://www.aulro.com/afvb/discovery-...-tweeters.html