Rusty Buglense?

Of all parts to take for granted when it comes to rust, it is the heavy glass of the bug lense.. but oh no, look what was hiding behind bright eyes..This is out of my 87, had vapors in it as usual. This one will need sanding, high temp epoxy, then the convection oven. I have never encountered this type of rust. This was in front of the battery, drivers side, and there is some rust in other places there too. This must be a rare problem. I gave it the tap test, but even then, I can't do that too much for the reflective material on the inside. I will attempt the epoxy route, see how it does.Any other ingenuitive ideas?

The lense is good, want to save it for spare.