I replaced mine last year. I removed the wheels to get to the screws. Removed the carpet from one board and used it for a template.

Picked up a sheet of 1/2" treated plywood, gray marine carpet and adhesive from Lowe's. I glued the carpet to the boards and used stainless staples to secure the edges.

Screwed the back on the trailer with stainless wood screws. They turned out really good and look factory. No problem doing it with the boat on the trailer.