Hey Ryan,
Yes, my truck did come without carpet. Remember, I bought Big Red in February of '08. It's an '07. It was one of two '07s left on the lot, since they were getting rid of the older inventory I received $12,000 off the MSRP. At first I thought I would miss the carpet, I didn't have much of a choice if I wanted this deal, after a while I am so glad that the carpet was not part of my rig. With all of the rain, mud, snow, and dust that I could track in my truck it is much easier to keep clean. In my old truck mud turning to dust was a constant battle even with mats. Here's another feature of the rubber/plastic floor covering, when installing the crossovers for the component speakers in the doors we just used velcro under the seats, therefore avoiding drilling into the floor and creating an access point for rust. As for mounting a fire extinguisher, look into those low level tool boxes that ride below the bed rails and won't interfere with your cover. That's where I keep mine, there not to expensive so I replace them once a year just to be sure it's in good condition.
By the way "Big Red" is not an FX4, she's a Limited Edition STX Off Road model with a 4.6HO engine. They did not make very many of these 3v 4.6s until the end of the model year. Now this engine is a build option. I was lucky it was still available.
Later...