Interesting advice to rinse it off. I wonder if the tap water really has significantly less dissolved salts than the rain water. Rain water is where the tap water comes from after all. Granted it's filtered by natural and made processes first but I don't know if low levels of dissolved salt are something they care about removing. Small amounts of chlorine are often added.

I just wonder if most of the salt exposure comes from the air rather than the rain. Rinsing the bike off occasionally would help but so would just letting it get rained on.

My experience from a non-marine climate is that leaving unpainted/untreated steel exposed to the elements will cause it to rust. A chain that is lubricated and used regularly won't rust. Many bolts/screws on your bike can be replaced with stainless steel equivalents from the hardware store for pretty cheap. Those are the things tend to rust. You can also put a light coating of oil/lubricant on them.

Carrying around and putting a cover on your bike seems like a pain to me, - but I'm lazy.

FWIW I have a brother that lives in Hawaii and rides a 40 year old Peugeot. I doubt he covers it up. I haven't seen it in awhile but I know it's got some rust on it. If I remember right he complained about having to leaving outside in a rack back in his college days. My guess is that it got scratched up and that's where the rust got started.

As a visitor there I'm always struck by how some things seem to deteriorate so much quicker in that climate while other things tend to look newer for longer.

I'm not sure how a cover would hurt anything if it's fastened in a way that the wind won't cause it to scuff up your bike.