Question about paintjobs

[JAKES 68GMC]

I've got a question about re-painting my truck. My paint now is flat for the most part and really chalky. So I'm planning to paint it gloss hunter green Rustoleum sometime in the near future. It won't be a perfect paintjob, but I'm hoping it will look good and last awhile. (it's a long shot, I know ) So, my question is, as a daily driver, how long would it be before the paint starts to fade and get chalky?? I probably won't add a clear coat, but I may add some hardener to get a better finish. Thanks for the replies.