It's been so long since I did those projects, I honestly don't remember how long they lasted. I don't believe I had any problems with warping, but that might be me wishful thinking.
Wouldn't the stain/paint finish help with warping?
I think either a dutch lap or a shiplap siding would work just fine for that application. In fact, a horizontal fencing might look cool. If N put a cap piece over it, I think it would do great.
My experience has been, make sure the wood is DRY before sealing. I went to a lot of work one summer building a deck for my mother with wood that wasn't as dried as I was told it was. It rotted from the inside out within a few years.
I'm building some benches for my son and daughter in law, and I' frustrated that the wood is too wet to stain. I think the benches will have to be stored in the garage for the winter while I wait for the wood to dry.
I don't want a repeat of what happened with the deck.
