Mine has very bad roof rust and I'm cutting all the rusted through portions out of the roof skin. This allowed me access to the areas inside where the glue was applied, so I could clean it all out and POR 15 it. I'll never have rust again.
Here you can see the joint where the roof brace was glued into the side of the roof frame and the roof skin. This is exactly what I saw when I cut the square out of the roof.
This is after some vacuuming
And here's after some cutting and grinding. I have a small 1HP Shop Vac I used with an attachment and a Zaxby's straw to get every last little bit of loose rust out of there. It worked well.
Last step is POR-15. Rust shouldn't be a problem anymore.
Here's all the spots I cut out.
I did cut all the roof braces. I intend to remake them with regular sheet metal and glue them in with 3M Window Weld urethane.
Here's a close up of the culprit. The glue turns hard and black.
At the end of the day I had cut a lot out of the roof. Here's hoping it all goes back well!