According to my body man, these rust primarily because the drains get clogged. They outlet behind the rocker panels and are easily stopped up. Check those regularly and it should help. The sunroof and windows drain to the same place.
I have two complete windows with all metal if anyone needs them. Will get some pictures and post. There is some rust on the but the metal could be cleaned and painted. They don’t need disassembly so they should last a while.