Insulation in the construction trailer, vapor barrier yes/no?

Hello, a vehicle like that can be very well insulated with XPS or self-adhesive Xtreme Isolator. Vapor barriers are not installed there. For cost reasons, I would bond and seal XPS directly/form-fit from the inside with Würth. This is how caravans have been factory-equipped winterproof for decades. We have our caravan in the Alps in winter. minus 25 is absolutely no problem. Important are forced ventilation and ventilated furniture construction, as well as a warm air heating that distributes the heat all around with a hose. With only a stove, corners can become damp.