I'm a little late to the party, but I have used Evaporust. I wouldn't consider using it for a floor pan, because it needs to be completely wetted for quite a while (they recommend using paper towels). Even then it's hard to keep it wetted. AND it needs to be rinsed off. It leaves a black residue that isn't real well attached to the base metal, so it has to be rinsed/scrubbed off.
But for small parts, it works very well IMO. If you can completely submerge the parts, that's a good application for Evaporust. Then what I do is rinse and scrub them with a hand-held wire brush.
But for a floor pan, a wire wheel is the ticket, followed by a rust converting primer and topcoat.
