I need to replace the bunk boards on my trailer, and wood is the obvious choice, but what about that composite stuff that is used on outdoor decks? It's available at any big lumber yard, and will never rot or warp. Is it strong enough? My trailer currently uses carpeted 2x6's. Anybody ever tried this?

The decking material is not up to the task. Bends too easy. There is likely a stiffer/thicker composite out there somewhere. I think your right about finding a better option than wood though.