I am installing 1x6 V Groove Pine Tongue & Groove on the ceiling of a new patio cover that I have built. I intend to stain this with a Minwax stain. What would be the best to protect this with as far as urethane coatings is concerned. What I have in mind is to cover the stain with Spar Urethane. I live in South Louisiana where it is quite humid. The gable end will remain open as I intend to install glass panes in the future if I close the patio in. For now it will be used as an open patio.
I wouldn't varnish it, because any varnish will eventually peel, and then you'll have a real mess. Just stain it with an exterior stain, like Cabot. (not minwax furniture stain). That's how porch ceilings are done around here.