64 valiant floor pan rust, practical fix?

Are the read floors just surface rust? And that evaporust mixture is super cheap to make and works better than the real stuff.. would clean most of that up in a few hours
On mine the back ones are for the most part and I cleaned them and just sprayed rust reformer , not knowing when I'd get to working on the interior. Which I'm still no,t but will have to take care of this problem . The fronts are a different story .