Thanks Kenny.Looking good!
My suggestion is to use rough sawn white oak, call some local lumber/saw mills and inquiry about it, I did my 16' trailer for about $180 last year. After it's dried good, paint it with used engine oil to waterproof it. PT lumber is hard on the steel framing and screws it touches, and it shrinks a bunch when drying.
After I did my research I found everything you said to be exactly what my research turned up.