I've replaced my 2001 model bunks twice ( almost 18 years) with 3rd set still good. I've used 2 x 4's and cut to original lengths. Bought the carpeting and Thompson's water seal. Also bought ss staples and lag screws. Prepped the bunks cut and covered with the carpet (leaving 1 1/2" un-covered bottom of bunk).
Took the new bunks to the ramp, launched the boat and had the new bunks on in 40 min.'s. Yes, also mid-week with very little ramp traffic.
6 years now on those bunks and still in perfect shape. Original bunks were the worst (3 yrs).
Every time I park the truck/trailer I check all 4 bunks thoroughly. Funny. I rarely see anyone else do that! To me it's just another maintenance issue to replace bunks. But, after original bunks you'll get many years with re-placements.