Some bicycles get rode into or through lots of deep water, other bicycles often get left out in the rain and foggy weather.
Any which way, bicycles can most definitely rust from the inside out, so are there any recommended ways to protect against the elements?
Spray/pour ACF-50 in the frame prior to assembly. Drain, wipe, assemble. I did this to my Soma Double Cross. That would probably not make a frame weatherproof if left under the rain regularly. If you want to have a DGAF frame that can withstand any amount of water at any frequency, you need an aluminum frame.