Carpet Concept - Reflectix is Worthless

[Boyntonstu]

The Reflectix is good for reflecting the heat away. I have used it before, and it did help keep things cooler, but nothing like having actual insulation behind it. 
Just a thought, why not use 1/4 or 1/2 inch Polyiso covered with Reflectix, and cut to make a tight fit in the windows?

Reflectix IS an insulator... with an R value of 1.1, but it can be doubled and the R value is cumulative with each layer and air space.  While it may not have the R value of fiberglass batting, when installed properly is IS better than no insulation at all.

https://www.reflectixinc.com/about-refle...formation/

Having had travel trailers with neoprene (Scamp Elephant Hide,) reflectix and rat fur carpet (Later model Scamps,) and standard residential fiberglass (Sac City Burro 17) I can tell you that any insulation is better than none, and even yet the majority of heat loss or gain is through the windows.  Dual thermopane windows are worth their weight when it comes to keeping an interior warm or cool.

I live in SE Florida where no insulation is installed in the walls or the windows; only roof insulation.  
Double insulated glass is seldom seen.
For roofs, insulation R values of 13 to 20 are common.

In our super insulated house in Maryland we used low e double glass windows, 6" wall insulation, and two 1/2" reflective foam boards on the exterior.
It was amazingly efficient.

Why not insulate walls and windows?  The Heat Transfer equation is Heat= MS (T2-T1).
Heat travels from the higher Temp to the lower Temp.  Never the other way.
Ice does not cool your beer, the beer warms the ice and the Heat coming out of the beer leaves it cooler.
At 95*F the house needs 20*F of cooling to to counter the heat coming though the walls and the windows to yield a comfortable 75*F.
We insulate the attic because without insulation the temperature in the attic can easily reach 120*F.
We would need to cool 120*-75* or 45*F, over twice the heat load of the walls/windows.


Back to vans:  A carpet with a gap behind it on all steel areas would feel OK.
For windows, either Reflectix, Reflectix adhered to a foam insulator, a reflective tint, and/or the carpet flap covering it.  I understand that there is a new window tint that appears transparent but which reflects heat.  
An exterior shade or awning to block the sun would be perfect.

As for the van with solar, a 1" gap beneath the panels would shadow the roof and make it much cooler.  
The 1" gap would be a handy place to store pull-out shades for the side windows.

Interior Finish Materials R Values
Gypsum Board (drywall 1/2")
0.45
Single Glass
0.91
w/storm
2.00
Double insulating glass (3/16") air space
1.61

My $0.02