Let's call it 'utility chic'
Hey thanks for the encouragement everyone.
Well, I've been getting in little bits of time here and there but this process is so loud I have to work around the kiddos sleeping, and I got sidelined by a goat feeder project

, but I finally have something worth updating you with.
The hammer and die approach was a partial success. The profile of the rib it created was really good--it was controlling it down the length of the floor that was a huge challenge. I spent some time working out a jig (a track essentially) to keep it going straight while I hammered the die, and you had to hit it very squarely to keep it from digging in and making a major corner dent. AND, you had to hit that thing HARD!!! I used a 6-8lb. splitting maul and I really had to wallop it to produce a nice profile. Well, we're working with 16 gauge here. Here's what's left of the die--probably one more floor in there:
http://i132.photobucket.com/albums/q35/duffontap/jig.jpg
If I currently had access to heat, I would have used Bikersmurf's suggestion to see if it would have made it easier.
Since this was really a major experiment, I wasn't prepared for the insane panel warpage. I went to bed last night with nothing to show for my work but what looked like a large, inedible potato chip. A lot more hammering, flexing, hammering, and a lot more hammering and some hammering and it would finally lay pretty flat. The corrugation stiffens it a ton, which was the desired effect. Well, here's where I'm at right now:
http://i132.photobucket.com/albums/q35/duffontap/Floor1.jpg
Here's a small part that I thought turned out really good, and shows that it is possible, at least at random moments, to produce decent looking work with the hammer and die method.
http://i132.photobucket.com/albums/q35/duffontap/Ribs.jpg
Here's a pic of the back side. I wasn't even going for a specific depth, but I ended up right around OEM depth (+/- a dozen 1,000ths of an inch) on average.
http://i132.photobucket.com/albums/q35/duffontap/BackSide.jpg
You can see clearly in this one that I somehow mis-measured somewhere and got two ribs too close together. Good thing the whole floor looks like it has been beaten to death to distract your eye from details like that.
http://i132.photobucket.com/albums/q35/duffontap/FloorMore.jpg
(My 4-year-old daughter just looked over my shoulder and said, 'what's that garbage can doing there?').
I'm perfectly happy with the results. It was cheap and it will probably look fine under a thick coat of Raptor Liner, and even better under a mat. Alternatively, I could fabricate a back story about how this truck used to be owned by a small engine mechanic in Arizona who used it for deliveries for decades.