There is also trailer bunk carpeting. It is similar to indoor outdoor carpet that you might get at a big orange or blue box store. However, bunk carpet does not have a rubber or a light latex-y looking backing (as I've had both from the big box stores.) This facilitates water draining out of the bunk carpet, and drying, and therefore not rotting your wood bunks or pads as quickly as something that holds in water. It's also probably a bit slipperier than old house carpet scraps (which is always what seems to be half falling off of trailers when I buy a boat...

) You can get bunk carpet at West Marine stores, or order online, say here:
http://www.easternmarine.com/Boat-Trailer-Bunks-Bunk-Covers Unfortunately, the SBO store here doesn't seem to carry it, or I'd say order it here. You can attach the bunk carpet to the pads with either monel staples, or stainless steel staples. Honestly, I've found it easier to source monel staples (nickel alloy that resists corrosion.)