On youtube - there is a 5 minute long "Montana Construction" video published in 2009 from Keystone. At about the 4:22 mark they make a statement like "even our slide room floors are insulated with R14 astrofoil insulation and radiant technology in the ceiling. Most other brands don't even think about insulating the floors in their slide-outs." Things could have changed since 2009 - but the video can bee seen here...
Unfortunately I did not see any shots of the slide-out floor structure. I looked at a couple of other videos under the topic of "slide out floor repair." They were repairing floors on SOBs and they did not reveal the structure framing. The floor unit was already a buttoned up ready to be inserted in the slide-out. All I came away with is the most slide-out floors appear to be a framed unit that look to be about 2" thick. For Montana I would assume it to be some sort of welded aluminum tube frame with plywood on top and bottom, with rigid board insulation between the plywood...but that is pure speculation on my part.