I thought I would experiment with mine. Painted the entire floor with a Rust killing paint then went a bit crazy. Batons with 5mm foil back foam between them, then a multi foil insulation product over the batons, then the ply (forget how thick), then another 5mm layer of foam, then rubber flooring, then carpet in the no shoes section of the van.
An the verdict is... its still cold as feck when I stand on it bare foot. Think I would just use celotext/kingspan type stuff between the batons instead of the foam and multi foil if I did it again.