Finally, regarding the story Great Rao suggested
"Superman Under the Red Sun!", I think a page must have been omitted from the story. Does anyone know what the Red Kryptonite did?
There's no missing pages from that story; that's how it was originally presented (I have the original, which matches what was used on this site). Confusing, isn't it?
I think what was supposed to happen in the last panel on page 13 was that Superman exposes himself to the red kryptonite, which then makes him tiny enough for the rocket ship. Then the comment on page 14 makes sense, where he says he just needs to wait for the red kryptonite to wear off. Why they inserted the bit about the shrinking ray, who knows (probably poor editing).
I think when they reprinted this in Best of DC #1 in 1979, they apparently fixed it (my copy isn't handy).
Another possible Red Sun story is Action #350, "The Secret of the Stone-Age Superman", where he travels back in time. See
here.