Hello and welcome to Just Answer, my name is XXXXX XXXXX I will assist you with your question.
Ford's rust thru warranty is for 5 years from the original date of sale, however, you can contact you local dealer and discuss this with them and they may offer to help you with it. I know for a fact that they will not cover the complete repair, but if you are a good customer (they judge this by how many new vehicles you have bought from Ford and your service history) They just may offer you assistance. The only 10 year Ford has out is on the diesel engine warranty.
If you don't have much luck with your local dealer you can contact Ford directly, there consumer relationship hotline number is 800-392-3673.
If you have any more questions or need more assistance with this issue, just respond and I will get back to you as soon as I can.
Thank you and have a great day.