There is no need for PT wood on a trailer deck. If I were replacing a deck today I would use Oak planks and give them a couple of coats of a good UV sealant. Then, after installation, I would undercoat with a rubberized automotive undercoating.
Clean and recoat the deck surface with a UV sealant every couple of years and the new deck should outlast you.
Clean and recoat the deck surface with a UV sealant every couple of years and the new deck should outlast you.