I buy air - dried black locust from a near by mill.
The locust is full 1 inch thick have no problems with it warping.
Most boards are 6 inches wide and I cut edge of boards at a 15 - 45 degree angle , and use Kreg pocket hole joinery to make wider boards - usually 24" 30 " wide.
Prefer to use Dap 50 year caulk . I think it is important to seal with caulk that remains flexible for a good seal.