Your situation is like mine. We do what we can with the best tools and know-how we got. I appreciate the pros more than ever before.I've been debating this too. I've gone over the cargo area and found almost not rust. What I little I did find, I scuffed to expose it and treated with "Black Star". Planning to treat the entire undercarriage with it too.
The Mega Mat is VERY sticky. Getting it up would be difficult to say the least. But, at this point at least, I'm planning to line the entire floor and wells. In five years, I might regret it, but hopefully the pre-work that I'm putting in will help a good deal.
All the best,
O.N.