No perfect method
There is no perfect method of insulating your box, there are only compromises. Remember this is a boat and with that comes trade-offs. Polyurethane foam is the best insulation medium for the value. It is easy to work with when purchased in sheets and provides for adequate insulation. The vacuum panels are expensive and very effective but are not tollerant of mistakes during installation or afterwards. Mistakes like punching a hole in the panel with a mounting screw or sharp object.
