There was another thread here recently, but I also used pink foam board (2") covered only with the horse stall matts. I used to have 3" of plywood carriage bolted through my flatbed. After 100K miles of riding on the flatbed, that plywood kept moisture soaked in enough that the bed was fairly rusty when I took it out. If you take the camper off all the time and remove the plywood, it probably wouldn't be an issue, but I like the lighter weight, better insulating, non-moisture absorbing foam + rubber matt idea the best. At least for now....we'll see how it goes for the next 100K miles.
