If I was going to use por15 buddy I'd just sand it down and do it with por15, or maybe if you got the cash use their marine clean to clean it and then use their metal ready to "etch and make sure it's done right.
HOWEVER, I used it on my monte carlo floor and all I done was take a wire brush wheels on a grinder to all it and then vacuum the dust, and paint it with por15, it did peel in some spots were it was paint only but the rusty areas it held tight as can be and never came loose. I didn't have the cash for all their stuff but for you a quart would absolutely do your entire floor and some more. A quart did my MC floor pan from door to doo firewall to trunk,2 coats as rec. by por15. I had a little bit left. zerorust is basically the same stuff and may be cheaper, check raybuck auto or google search for it and compare. I also heard good things about miracle paint, stacey david from trucks and gearz now uses it alot and said it was good stuff.
Now if you don't get all the por15 prep stuff, you might sand it down with like 120 or 180 to get it scuffed pretty rough to get a good bite, which may work in place of the metal ready and might wipe it down afterwards with grease and wax remover, which might work in place of marine clean. If it was me and I didn't have the cash it's what I'd do.
You'd only need to prime if you were going to use regualr paint or something. You won't need a topcoat on the por15 either since sun never hits the floor areas with carpet down.
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