I believe the main flooring on my rig [20 29RS] is a sandwich wood/foam/wood. Not certain how thick the wood layers are but I do not think they are that thick. I believe the slides are the standard thick stuff. If I look in the basement and take off the side panels, I can see the actual wood/foam flooring, but I do not know if it runs the entire length of the rig.
I've looked into this because I want to build a bike rack inside to store it while driving. I am not satisfied that the floor is thick enough to hold the screws needed for my satisfaction. When you have a bicycle that would cost $14k to replace, you understand why you would want to store it inside while traveling. That and the wife does not like it on the bed like it is now.