Insulation won't last either all day or all night, so you still need at least heating, and at least a fan if not a 12 volt air conditioner. I heat and cook with kerosene because it is cheaper and drier than propane. I have a window van with no added insulation, and if the temperature dips below freezing, I run my heat all night long. Where I winter it can remain below freezing, down to -40 or so, for months in a row. Still my yearly heating/cooking fuel cost is usually $50-$60(USD). Insulation couldn't keep me any more comfortable, and would take many many years just to pay for itself. Insulation can also trap moisture and cause mold & rust problems. Insulation only slightly slows the inevitable, because a vehicle has so much outside wall space compared to very little interior space. It's your heating/cooling power that actually keeps you comfortable, not insulation.
When I had a panel van, it was a huge target for thieves, hoping they could get tools or other easy to sell items. Since I switched to a window van, I have never had a break in, but in all fairness, I make it a priority to make sure nothing worth breaking in for is ever visable to anyone looking. My laptop & valuables stay hidden from sight when not in use. Only some clothes and bedding are obvious, so nothing of any immediate interest to thieves. Window vans aren't normally associated with anything thieves want any way. Life's a gamble, but you can play the odds. So far window vans have been the best winners for me.