I am not worried about fixing the bunks. It's the fenders.
OH, the inner fenders? That's usually carpet on plastic. You can install that too pretty easy. Just wrap it around and staple it on. The fenders are held on with bolts but they might be rusted. If so, cut them off with a hacksaw or a dremel and replace them with some stainless bolts and locknuts from Ace hardware (about $3.00)
I just had to do this 2 years ago on mine.