rear quarters, up underneath and inside them, rockers, bottoms of fenders, floors, tails just in front of back bumper yeah
major rot areas, bad on the burbs, burbs are the rustiest ones of them all, they hold so much water and muck its not anywhere near funny
being in FL doesnt prevent it from rusting any much more than up here, down there is sand and sand and sand and if it was anywhere near coastal areas then they say that salty air moisture kills the metal just as bad as up here with salted roads mushy sloppy slush crap all winter packed into body panels
inspect very closely from up underneath the truck, flashlight and all, flat thin fridge magnet run over body panels slide around and see if falls off the body skin anywhere where bondo may be
also check spring packs in centers between u bolts for cracked leaves, look closely, make sure packs are uniform and ends of leaves are all orderly and inline and straight and all bushings in places on ends of leaves, if not then most likely has been run hard not taken care of and id be scared then,
look for gov lok junk too
pull pvc valve and check for exhaust gas pressure in crankcase while engine is running, if there is any then run away fast, bad rings and.or valves or hole in piston,
good luck