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The little rust you see on the floor is most likely easily patched. I'd pay particular attention to the frame rails, namely near the front suspension mounting points, and also the torsion bar cross members. Like all good 60's mopars, you need to check out the rear frame rails also. Don't be afraid to poke them with a screwdriver, especially if you see fresh undercoating on them.
Hopefully others that have 65's can chime in with any other spots to be on lookout for.
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look for rustbehind the rear wheel well the quarter rolls under and they pick up a lot aof rock chips also any moisture in the trunk seems to find its way there the lower front fenders look like they got a little rust in them biggest deal do your homework and make sure the trim is all there along with the lights this is a one year body style and finding repair panels and trim can be a challenge overall looks like a good car and if all the parts are there not outrageous on the price
Check the cowl for rust too