I insulated virtually the entire surface of my Westy except for the poptop.
I insulated the floor, the area over and in front of th engine, all of the
doors and under the front floor and over the heat shield. The area behind
the refrigerator and cabinets was already insulted with fibreglass. I also
added about a dozen cans of undercoating over already existing
undercoating. I gave special attention to the front wheel wells, under the
front area and around the heat shield.

My original intent was also to create some sound barrier and all of this
worked surprisingly well considering the bubble wrap is not intended to
reflect sound.

I also have a 5000 BTU catylitic heater behind the passenger seat. It has a
hose to route its waste to the outside so opening a window is not
necessary. My van is surprisingly cozy and warm. The upper bunk is not
insulted and is, or course, a bit cold but I use a goose down insulated
sleeping bag if I have a guest in cold weather.

I haven't yet used the van on a very cold Wisconsin winter night but will
do so soon. So far, my cold nights have only been in the low 30's

About insulating the upper bunk with this bubble stuff, assuming I solve
the adhesion issue, how well does this stuff fold up when the van top is
dropped for travel. Or is it necessary to remove the foil to travel--would
seem like a very awkward arrangement.

Good luck. This site is tremendously helpful to me.