nonsense... I have a 5th gen accord and there most certainly is a hole in the firewall on the passenger side. There is a rubber gromet right in the center, about 10 inches off the floor. A bunch of other cables already go through this gromet, so you'll have to work it to get it through, but you can do it.
And yes, if you have a sealed box thats falling apart, its gonna sound like crap. Ported boxes are designed specifically to maximize SPL, but sealed boxes with holes maximize nothing.