I have a 1997 Xplorer 230XL. Last year I noticed a small amount of surface rust on my low side just above the running boards in front of the rear wheel well. I used my Dremel tool to remove the rust...
I do not think there is a way to spray the backside of these panels, except now with the holes there. As I said the repair guy is going to spray something in there when he cuts out the bad. As my post indicated, I expect to have to do this again in the future.