I like the idea of using some type of spray on rubber on the camper itself. Next time I take mine off I'm going to seriously consider it. Just repainted this last time though so its going to be a while.
Mine came with a stall mat too. It is cut to fit between the bed mounting bars from fwc. I also use the tacoma bed mat on top of it all for a level surface. My turnbuckles do loosen up once in a while but i appreciate the shock absorbing effect of the mats for the miles of off road travel I put my rig through.
My camper is only on my truck for trips so I don't worry much about water below the camper.
Debatable.
My turnbuckles loosen on most trips. Might be due to variables such as truck type, camper type, and the roads driven. I just tighten them up when I make camp.