I just put the puzzle pieces together and jammed them into place, laying them on top of plywood. I was lucky in that the width was almost perfect, just a little tight. The length is about a quarter inch too long and I was hoping it would crush down but I think I will trim off a bit on the front wall end, because the door is very tight now. It took more time to unload all the stuff in the trailer than to install the flooring.
I got the 5/8" flooring, which seems to be about right.
http://www.amazon.com/gp/product/B00DGCDYR0/ I slept in the trailer overnight, the low was 32F. I don't think the new flooring changed how cold it got in the trailer, but it is much warmer on the feet than cold plywood. It is much easier on the knees.
It covered up the cable hatch in the floor, which I use for an air intake vent (crack the roof vent, open the cable hatch). I may have to cut a circle shaped flap in the flooring to allow the cable hatch to be opened and used as a vent.
I am very surprised how comfortable it can be to sleep outside in an unheated trailer in cold weather. I always thought that temps under 50F would be very difficult. But with a 4" foam mattress, a 20F down bag and a fleece blanket covering the top of my head, it was very comfortable. I forgot it was cold out until I stuck my arm outside of the sleeping bag.