Mike,
I thought we has it bad regarding rust up here in Massachusetts but that salt air is a killer.
I'd say it would still be a 5000 no matter what parts are transplanted into it or from it so keep the faith alive. Maybe you can use both doors on a 1000 series Genesis and call it a 2500
Your post got me nervous as my doors are also loose on mine as a couple plastic bushings are missing and well as a rusted lower support bar so I gave it some love with some duct tape-
I have some time off in a couple weeks as my Wife and Daughter are leaving the Country for a week so I hope to finally get started on the restore.
Jeff