We'll have thermorests, and flat boards to make it a better (non ribbed) surface.
lol, LOTS, and every ounce of water from our breath, probably. Ventilation can be easily added to the center "hatch" section, as it is also the highpoint.
My brother and I plan to sleep in there. The nice thing about being on the floor of the canoe, you have zero concern about tipping as you toss at turn; your weight is at the water line. The material is light and velcros to the gunwales, so if something does happen, we won't be trapped.
First use will be on Michigan's Ausable river, overnight lows in the 50s. The original plan was for 76mi from Mio to the mouth at Lake Huron in 2 days. The distance got halved after some female intervention, though. lol
Edit: The boat will be anchored at the inside of a bend in the river, not adrift. lol