I had my single 10" woofer in my box in the trunk without any porting, you could feel it, but barely hear it.

Sound is definately much better ported into the cabin through the first aid box.

I think with one 12, try it first and if y ou dont like it you can always cut and port later.

Alon

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'92 300CE - Sold
2004 C240 - 744 - C7 Wheels - Android Radio
2002 C320 - 816 - Sport Wagon