I got the plastic interior panels for my Sami, i got my through EBay and they were a hell of a lot cheaper than what other vendors were charging. The plastic panels have no structure what so ever, i altered mine a bit so they wouldn't vibrate and make noise. The little plastic plugs they send you to hold the panels in just dont do the job. I ended up getting rid of the plastic plugs and replacing them with some nutserts, button head screws, and some finish washers and it looks pretty good.
If you want make the tail gate house speakers i would make my own out of some sort of metal. The tail gate is pretty darn simple.
Amilla