I have 2 campable tiny trailers and I placed 1 1/2 " of blue foam board
( two layers of 3/4 ) on the sub floor and covered the foam with a layer of 7/16 osb to protect it. It is simply layed in the trailer the only thing that holds mine in place is a small baseboard around the perimeter.
I added foam backed commercial carpeting to one of the trailers as it is a walk in rather than a tear.
An addition of this type will add about 1 1/2 hours to a build to cut and fit everything and will cost $40 to $50 +/- .
I went into the album and found a picture that shows the foam insulation layer.
Yes I put down some laminate flooring in the galley and track off area the carpet starts at the galley wall and covers the sofa / bed area only.
I small throw rug can be placed on the laminate to wipe off feet or remove muddy shoes before entering the carpeted area.