oops is right no doubt,but if you cant or wont put that much time in it spray foam in a can topped off with bondo covers the holes for awhile.I have used the foam (great stuff ) to fill holes that are constantly getting full of mud.The foam keeps the mud out.I dont know yet if the foam makes the rust any better or worse,but I know it keeps water and mud out.I would not do this to a nice truck but it does the job on a beater

oh what a feeling:
#1 86 xtra cab 22R,EB 261 cam ,Hooker header,2" ex with cherry bomb, Aussie powered
#2 86 sr5 4x4 efi parts truck
#3 87 2wd parts truck
84 supra yard art