I saw this product on Shipshape TV and thought it looked sturdy enough to serve as trailer bunks. Did a dealer search and found that Oswald lumber in Leesville SC carries them, so they must be readily available. Don't know what they cost, but no more than you would need it might be worth it to never have to replace due to rotting. Just replaced mine last year, but will check these out next time I need some. They come in larger sizes too in case the 2X4 is not big enough.

http://www.lumberock.com/2x4_deck.php

SeaRay