If you're going to use the product in a few days, use a single layer of a sandwich baggy between the lid and can, it will keep the lid from "welding" itself to the can.
My dad always used waxed paper and I continue that process today with paint can lids.
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Jim
Sometime life gets in the way of living.......
I have owned a paint store for 25 years and I love Por 15. It does loose its sheen but so did car paint till clear coating came. Rustoleum will loose its sheen also. In my experience I have never seen a paint that dries so hard, so fast and it is actually brushable and self leveling.
I have used POR15 with good results on numerous projects. The secret is to clean it well, use the metal etching to allow the paint to "grip", and then the POR 15 coating. It is difficult to remove even when you try to sandblast it off.