The first priority is air leaks, not insulation. A small air leak will chill
the interior more than a LOT of insulation will make up for.
Of course you have to have some air exchange, but it's better to have it
under your control rather than leaving it up to infiltration.
My trailer became quite noticeably warmer after sealing with plumber's putty
around the grommets of the where the wires go to the converter from the
interior.
Al Grayson