Have fun getting back in there if you glass in the bottom of the camper. That's a horrible idea. Like screwing the door shut on your house. Why?
And a layer of PT lumber on the bottom of your camper is not going to give you cancer...more paranoia. But not sure it's needed.
But bottom line, how long has it lasted until now? Do you really think it will fall apart in the near future? And if your truck bed is pooling water ( it's not becasue it's a flatbed and if it is, drill a couple holes in the bed).
I just saved you a weekends worth of work!
