Another vote for needing the batteries correctly connected and charged for the slides to work. My Cedar Creek 36CKTS came with 4 six volt batteries and they weren't connected correctly. They were connected as per the diagram in the battery box, but they didn't work that way and neither did the slides. The 6 point jack system struggled but it did work. It didn't matter if we were plugged in or not. After going back and forth via email with Forest River, I got a diagram from them on how to hook up the batteries and then everything worked fine.
As for the insulation, sounds like someone pulled a fast one on your BIL. I just had to get under mine last week (warranty ran out last month of course). Mine had a thick layer of insulation and the quilted foil liner above the belly pans. I assume that foil is there to keep highway water from getting in there, but I can tell you they sure as hell hold water INSIDE quite well.