Insulation will help to keep it warm or cool from external excesses, but we're treating it like a house (or a big caravan) with this idea which is probably all wrong. The worst culprit in a house's heat loss is actually through ventilation via air leaks in the fabric. Living in a tiny enclosed space like a van will create plenty of that each time you get in and out, but you also have a lot of moisture around through breath and cooking compared to a house's larger space,(especially at night, all closed up) which will make very wet air, which will tend to deposit onto cold surfaces (e.g morning windscreens). This condensation can cause all sorts of problems from rust, rot, and fungal diseases or asthma, especially if it can stay trapped in tight, badly ventilated spaces. It can only be prevented by meticulous airtightness. Insulation on a big building will save some energy use during the long continuous winter, but as long as you have the power to overcome the campervan heat losses (which the Cali does), you are better off with good ventilation (air vents in roof) and nice heat to keep warm. I have serious doubts that any added insulation to a van will do any good, but more likely harm. Sprayed onto bare metal in an airtight way, may have a more useful effect.
Sounds to me like the Cali is well designed in respect of this issue.
In our old van, we used a 400w "small office" convection heater on the EHU all night, and this did the trick at no extra relative cost, unlike home use. The screen was nearly always completely dry. Those without the diesel heater could try this. Place the heater in the passenger footwell. They are pretty safe if not covered or touching anything.
Unless someone does a Phd like-for-like comparison, it's best to forget about this subject and move on !
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