Saturn trunk rattles

I have a 95 Saturn SL2 with the reflector taillight panel on the trunk lid.  I dropped a couple 12's in the trunk and now it sounds like I'm dragging around a bunch of cans.  Anyone else been successful in quieting one of these rattle boxes down? 

So far I have taken out the taillight reflector panel, taken it completely apart and put silicone in all the cracks and spaces and that made it solid.  Next I took off the lower trunk skin and put some silicone in there and that seemed to quiet that part down.  I got some Great Stuff foam the other day and sprayed some in some of the spaces inside the trunk lid, but I didnt want to get crazy and end up buckling the outer skin, so I didnt use all that much.  I took off the reflector panel and filled up some of the space in there with the foam, but it didnt seem to change it rattling against the trunk skin that much.  I glued the license plate and frame together and put a pad of Great Stuff behind it and now thats quiet. 

It seems like the more rattles I get rid of the more pop up.  Im looking for suggestions for my next step.  I'm thinking a Dynamat/B-Quiet type product but this car audio stuff has to take a backseat to my family so I want to try the cheapest alternatives first.  I've been told that the roofing stuff is very similar to Dynamat, with the main difference being their adhesion properties.  I live in So Cal so the summer temps and it falling off are a concern.  Maybe I could use the roofing stuff on the bottom and sides of the trunk, and get a couple feet of the good stuff for the trunk lid?

Any suggestions?  Should I try something else first?  Anyone?  ANYONE?!?!:)   Thanks!

Problem is, you can't take the cheapest alternative measures first - and if it doesn't work well enough - then go to the tried-and-true method of sheet metal damping using Raamat, B-Quiet, Dynamat and the like.  Adhesion with any brand should never be a problem if the metal is cleaned first with denatured alcohol.  I use a very cheap no-name damping sheet that has a tendency to be a little less sticky than the name brands, but cleaning the metal and a quick spray of 3M spray glue solves all adhesion concerns.

https://www.mcmaster.com/ ...catalog page 3274 ... Adhesive backed damping sheets ... polymeric mastic #9709T19

And, install on a warm day, sheets lying in the sun for warm-up, applied with the rolling action of a seam roller.

I think maybe stevdart is right, besides I could probably spend as much in the long run on cheaper fixes than if I just went ahead and did it properly the first time.  Im going to go ahead and use the no-name stuff and shoot some 3M spray on it too, I figure its going to work just fine on the bottom and sides, if I find I start having adhesion problems on the trunk lid, I'll get some better known stuff. 

Another question... after I line the trunk with whatever I use, should that sort-of swallow up most of the vibrations?  I know it wont completly eliminate them, but should it at least quiet down the back half of the car? 

MastaN, Ive used the 3M spray undercoating before, I built a 5 sided  box for my truck and sealed it to the back wall of the cab for the 6th side, then I sprayed like 2 cans of the stuff inside the whole thing.  Smelled terrible for like a week or so, but the problem is, it never seemed to completely dry...after several years its still somewhat tacky.  Maybe being in the heat and not ever exposed to outside air  has prevented it from drying.  Not a concern inside the sealed box, but in my trunk it could be a nightmare. 

Thanks for the ideas!

Thanks stevdart, Im going to give this a try as soon as I source some materials.  Which brings me to my question for today...  Does anyone know where I might be able to pick up something like stevdart is describing locally?  And what would I call it so they will know what I'm talking about?  I've wandered around the local Lowes and Home Depot here and didnt see it, but I didnt ask because Im male, and we all know we dont ask for directions to anything...but seriously I didnt want to sound like an asshat trying to vaguely describe this stuff.  Oh, I guess it would be smart to mention locally means Riverside, Ca.

You won't find anything.  Use the source I gave you.  Just make up a business name and fill out the form online.  They ship from several warehouses nationwide within hours, and charge actual ground UPS cost.  Give them your credit card info on a secured web page...it couldn't be simpler.  When I ordered 3 sheets (36 sq ft) I got the box on my doorstep the next day and shipping was $11.  Charged to the Visa.

My business name was "_______ Customs".  That's easy.