I'm part of a college student engineering organization and we were just able to get a 2005 Ford Explorer for free. It's in good condition except for the roof which has rusted pretty badly due to years of not being used often and rain pooling on top.
We are able to store it under cover and aren't too worried about looks or absolute best practices, but we would like to keep the interior safe from possible water damage in the future and prevent anything from getting too bad on the roof.
What is the best way to cheaply slow the spread, seal, or fix a roof like this? I've heard coating it with flex seal will work well, but my question is how long will that last? I've included photos below.