Ed - I replaced mine a few years ago. Used treated lumber with Monel Staples. Home Depot outdoor carpet in tan (matched the prior pretty close). Used carpet glue for outdoor carpeting as recommended by the HD guys. Also replaced the lag screws with galvanized. All holding up well two years later.
I was lucky in that I had a place to dock my boat while I took my time and did everything from cutting the bunks to size, cutting carpet, gluing, stapling and letting dry. Then mounted the first new board matching to the unreplaced on the other side to make sure it all lined up well. Then did the other. If you aren't as lucky, just prep the boards in advance. Once they are ready, go to your local launch, put the boat in the water (don't forget the plug!), tie up in some out of the way spot and then swap the boards in the parking lot.
Best of luck - Jim