What Carl said. Sandblast it.
POR-15 site lists an epoxy putty - the only thing I can see there that would be a filler. Probably very similar to JB
Weld.
If you're worried about it over the winter, anything but epoxy primer won't give much protection against moisture and rust. Appearance wise, just degrease it and shoot it with some rattle can enamel. You're going to need to remove anything you put on later if you don't sandblast it.
