living in the rust belt, I can tell you that there is rust, and there is salt induced rust, don't confuse the two. If the truck came from a rual area where they tend to use more sand then salt then it should ok, plus with only 21K it hasn't seen much road time. If it came from a big city or near by and the previous owner didn't bother to flush the under body, then you might be surprised to see how much rust has acumilated, even with the low miles. Bottom line , it depends on how well the previous owner took care of it. My 2004 has a surprising amount of rust under it, came from Detroit with 52K and I don't think it ever saw a car wash. I'm in the middle of a lock out hub conversion on this truck and this is the first time I had to use a torch to remove the wheel bearing hub assembly, and I have removed quite a few rusted hubs and am aware of all the methods and tricks to getting them out. Ask the dealer to email you pics of the under carriage. Tell the dealer to give you the name and # of the previous owner. ( WI law requiers dealers to give it if asked for) call the previous owner and ask lots of questions, At this point they should have no reason not to tell you anything you want to know about the truck. Hope this helps, Doug