What is the "Penetrol" / "x-tender" / "floetrol" of acrylic two part epoxy?

I keep some partial filled cans of paint to touch up. However, the interior of the can under the lip rusts, sometimes very badly. I heard that I could just turn the can upside down during storage and it would prevent this. However, wouldn't that just allow the bottom to rust? Do you have a solution to this problem, other than use all of the paint at once? Is there some type of storage container that could be used to prevent the rusting, but still seal the container?

I have taken apart my 50 some year old Rockwell drill press, made a couple of repairs, cleaned it up, and, before reassembling, am ready to paint it as soon as it warms up a bit more. I intend to use Rustoleum Professional spray cans, which I have had very good results with, but am open to any suggestions and/or opinions. The base and table are cast iron, and I intend to primer them first. So, first of all, I plan to wipe everything down with mineral spirits before painting. Good? Secondly, the instructions say that I can spray the primer and follow immediately with paint. Any issues with this? I always thought, perhaps incorrectly, that because it dried so slow, I needed to wait several days to topcoat Rustoleum primer. On the other hand, things change, and I've been wrong before, so maybe am in this case. Finally, I'm a little concerned with getting to much paint build up on the head assembly, so am thinking of simply painting it, no primer. Bad call? I know, some pretty petty questions, but I want it to look good when I'm done, and am getting too old to do things over again, so appreciate any thoughts or comments.