There wasn't even a fire in the boatman's hut. Only 2-tatami-wide planks had been laid out. The two of them laid down on these planks and were asleep before they knew it.
I don't quite understand this sentence. I see two options:
1) These planks are something designed for sleeping on (maybe I'm missing a cultural reference). In which case, I'm happy with the use of 敷く.
2) These planks constitute the floor of the hut and are not specially designed for sleeping on. In this case I find 敷いてあった confusing. The translation of "to lay out" doesn't seem like a word that would be used other than when talking about building the hut. I feel that adding てある reinforces my thought that this is something that was done after the hut was built.
In summary, I would pick option 1) but I wonder if 板 is something more than just a plank of wood.