If you are routinely dunking this in salt then you're going to want to make sure you rinse it with fresh as often and apply something to help fight the rust.
The Line-X itself will prevent the rust on what its covering just fine, the major difference between regular and premium is they hit it with a UV Resistant Protector. Realistically all of these will eventually fade if left in the sun, the premium just lasts a lot longer before fading in the sun. The Regular version has been fine for me on my last two trucks. I've always used Access tonneau covers and both beds were still shiny (if not quite as glossy) when i traded them in. The only spots I lost some of the luster were where I actually hauled construction materials and such regularly.