The 3M Panel Adhesive is a quality product, and from my understanding will produce a bond that rivals welding. I used it on one of my quarter panels when I decided to redo it because I'd made a mistake during installation (my first time, and it was the first one I did). I don't have an opinion on using it for a structural piece like a floor pan, other than basically the same as how you feel about it - I think I would also prefer welding over the panel adhesive for floor pans.
As for sound deadener, I used RAAMat BXT and Ensolite - which is basically DynaMat without all of the Dynamat logos plastered everywhere (which oddly enough, is good for about 30% in cost savings). The price has come up a bit since I bought mine, but it's still cheaper than most of the other peel-n-stick products out there. A lot of the other guys have gone with spray-in or roll-in solutions (Lizard Skin, et al) and had really good luck - it just depends on what kind of application method and/or how much you want to spend. The
It's easy to apply: have the surface absolutely clean, test-fit and loosely trim if you get into a corner or similar, then peel the backing and stick it down. You don't need to, but I recommend getting a wallpaper seam roller and squish it down to better fit the contours. You're going to be putting carpet over it, after all, and the layers of materials add up, which can make putting things back in (like seats, consoles, etc.) not line up 100%.
Also, make sure you have all of the holes in the floor pans (center console mounting holes, seat belt mounting points, etc.) drilled and ready to go before putting down whatever sound deadener you go with. I forgot to punch the holes for my seat belts until just before I put my carpet in. The RAAMat made a bit of a sticky mess of my drill bits - not horrible... just enough of a PITA of having to clean them, rather than just toss 'em back in the box after punching the holes... ya know?
Here's the RAAMat going down.
It covers really well. Make sure to put any seam sealer or other treatments down before the 'mat (mine is covered in Rust Bullet Black Shell with 3M brush-on seam sealer in the junction areas). The roller is mostly just for the seams - I only had a few overlapped areas, but for the areas that butted up against each other, they recommend using some aluminum HVAC duct tape (the RAAMat BXT is a sound as well as a thermal barrier - the Ensolite is just to break up the sound and act as an insulator). I can't imagine not sealing up the edges making that much of a difference, but Hey - I'm not the expert so I followed the directions - you can't see the HVAC duct tape since it all blends together without having logos and whatnot everywhere.
Since I put down Jute-backed cut-pile carpet, I didn't bother putting in the factory-style asphalt pads or put Ensolite on the floors. I also installed just the BXT to the roof panels, between the cross members, added the factory-style insulation, and installed the headliner as normal. The roof used to sound all tinny when I'd knock on it, now it sounds like I'm thumping on a tank.
I haven't done the doors or inside the quarter-trim area yet, since I'm still not done with my universal power windows, but I'll be adding some BXT strips to the inside of the outer skins, and completely covering the inner panels with BXT and Ensolite. I'll be adding some BXT strips to the trunk pan, inside the quarters, and trunk lid, and then some Ensolite to the backside of the rear seat divider and under the package tray (since I'll have a box with a pair of 10" subs up under there soon). But beyond that, I'm thinking it's all sealed up pretty well.
37.5 square feet of coverage sounds like a lot. But in that first picture, you're looking at approximately 2/3 of the first pack of RAAMat I bought. I bought 3 packs altogether, because I wanted to make sure the road noise and temperature issues were minimized as much as possible. In that regard, spraying something like Lizard Skin might've been the quicker way to go. If I start running short while doing the doors or the trunk, I'll get some more - I don't want to be that guy whose trunk lid or taillight trim panel is "buzzing" when the subs are hitting.
Here's a link to their website. Check out the 'How-To' page - it's very informative.
http://www.raamaudio.com/
Hope this helps!
