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I'll have to write them to see if they forgot to install the carpet in mine. Cabela's sells marine carpet starting at $19.00 for a 3x6 piece.
How about something more like a rubber anti fatigue mat with the holes in it, like they use in a lot of entrances?
I don't think it is necesary, I have fished out of a clam 5600 for 12 years and never had any trouble slipping