Just go with treated pine. I haul equipment everyday. Unless you are heavy hauling steel tracks anything but pressure treated pine is overkill.

Redecked my utility trailer and gooseneck both a few years ago...used pressure treated from the local hardware store. I spray them both down every year with used oil/diesel mixture (top and bottom sides of the boards).

treated pin and after it dries, forget the diesel and go straight burnt motor oil. pour it to it and let it sit in the sun a few days, then pour it to it again about a year later. should be somebody else's problem before it's your prob again.