"One thing I really don't understand is how you can have healthy feet after several days of wet shoes and socks. I've always considered dry feet to be essential."

Dry them at the end of the day and put on dry socks, so they're wet in the daytime, but not at night.

For during the day, some folks use hydropel or bodyglide.
I have no experience at doing that; my limited experience with bodyglide to prevent blisters suggests to me that hydropel might be the better choice.