For our full monty, we are departing from standard here. We ordered an automotive insulation product called EZ Cool.
A student did a senior project and it required him to test a number of insulations and his very scientific looking results are here: http://www.lobucrod.com/Sr%20Project%20Report1.htm
Additionally, As i further investigated Reflectix I found that it isn't actually an insulation, but a radiant barrier. reflectix on its own only provides an R value of 1. the insulating properties come from the air space between layers; with a manufacturer recommended minimum of 3/4". This is a really great article that probably warrants its own thread:
I am going to use one layer of this ezcool which reports R values of:
Down = 13
Horizontal = 9.6
Up = 8.1
Which ends up being cheaper than 2 layers of reflectix. I AM still going to put spacers behind it. also EZ cool offers a discount for rolls of 3+ and will do better on shipping if the actual cost is lower.
I couldn't find any thread of other AIRSTREAMers using ezcool, but it does seeom that other vintage moho folks use it. Anyone with experience with this insulation? Thoughts on product or install?