I’m in the camp that says if it comes with a finished interior, it should be kept intact, and only the seats removed.
Passenger vehicles are designed to be both easily heated and cooled from the factory. We typically do so every time we drive them.
Passenger vehicles are also designed to handle moisture problems and prevent mold. Moisture is one of the biggest obstacles to overcome, and condensation can not be prevented or eliminated with the current metal or fiberglass skinned vehicles. Insulation tends to hide and/or trap moisture, which is the exact opposite of what we want or need, and since we need nearly constant ventilation to keep both ourselves and our vehicles healthy, insulation is of limited and questionable value at best.
I’m frequently an extreme weather camper, this winter it has gotten down to -57f degrees. Even with the needed constant ventilation, I was able to keep my van in the 70’s with no added insulation, and not insulating the windows either. All it takes is enough dry heat. Insulation does not provide either heating or cooling power, it only slightly slows the inevitable. Only enough heating or cooling power actually works, with or without insulation, to keep you comfortable. If it’s either hot or cold enough that you think you need insulation, insulation alone isn’t enough.
Passenger vehicles are already designed to provide a quiet and comfortable ride, unlike cargo vans that need to be insulated for sound deadening purposes. That’s just one of the many reasons that passenger vehicles make the best campers. Opening windows also eliminate the need for roof vents and provide better ventilation for much cheaper. With opening windows, a $20 fan can provide better ventilation than a $200+ roof vent.
"Just because everybody's doing it, doesn't make it right." ~ THOW (Tiny Home On Wheels)