I used the rubber backed carpet from Lowes.. If you go back to where their carpet is, they should have rolls bound up in plastic wrap. These are usually the remnants left over near the end of the roll. They don't count how many yards of carpet are on there, just estimate it and put a price on it. I bought one of the rolls because the sticker said $18. I got enough carpet out of that to do my whole boat and I have some left over, so they made a mistake!
I didn't go all the way to the edges in the front with my deck, I used the space between the deck and the sidewalls to hold a plano box or 2 on each side. I cut the carpet to the wood first though, then did a dry fit. If I had to make any cuts, I cut the board and then tucked the carpet and stapled it to the underside of the deck. It's better to have more carpet than not enough which is why I cut the carpet first. I think I ended up shaving about 1/4" off total (1/8 each side, or just a blade width)... but I didn't cut the board to be exact either, so you may be more or less
