Insulation is a personal thing.
some people install a vapour barrier, some don't
pros and cons for both
I when for sound deadening, followed by a reflective 10mm closed cell on the sound deadening, then i insulated my panels with a 4mm reflective closed cell.
in theory it gives me an air cavity between the outer van shell and interior panels, which is what i learnt from drafting houses.
So i when with it.