There is a reason that pressure treated lumber isn't used in interior spaces, it can be toxic and a health hazard. Painting new pressure treated lumber or sheet goods can be problematic as moisture content is high when shipped from the mill to the distribution outlet, i.e. where you buy it.
FWIW, I replaced all the paneling in my RV with Luan sheet goods and a couple pieces of flooring with 5/8" CDX plywood. The plywoods and paneling were coated, both sides and edges, with a flooring finish made for bowling alleys and gym floors. That finish does a good job of sealing the wood, as would any urethane finish or spar varnish.
I acquired the wood finish at my local recycling center. They typically have gallons of paint and finishes that are unused and the cost is perfect-$0.00.
