I still own one of those older Crestliners with wood trim
The wood is teak and will essentially never rot.
The proper treatment is to use a teak cleaner, then teak oil. When you are done the wood should have returned to a deep brown color from its current gray and be relatively water repellent. Do not varnish this wood.
The unfortunate side of this story is that it must be oiled almost yearly to maintain its color. I made a mistake one year and used too much oil on a couple of pieces and it stained the adjoining vinyl. So just make sure you clean up any excess immediately. The best way to do the job is to remove it from the boat, do the cleaning and oiling, and reattach. I have actually never done this
but plan to next winter.
BTW.. Seabrite (or something like that) oil and cleaner are available at Fleet Farm and it not too expensive.