Everybody line up single file....
After reading all the debate about Reflectix and knowing it was going to be in the 20s the next few nights I finally cut some for my windows and what a difference it made! It works fantastic as a barrier and blocked the cold coming in from the windows. Completely worth buying it. I'll definitely do it again for my next van but even with this half ass job I did last night it was still a big enough difference to notice.
However, it's not without a caveat; I can't tuck the edges under most of the plastic trim so I had to tape them in place and during the day remove most of them for driving and to let light in. That's going to get annoying really fast.
Also, just a word of advice: if you are going to use Reflectix on your windows and haven't started or completed your build yet it will be much more convenient to cut and fit the panels when you can actually get to the windows rather than after you have a bunch of stuff piled in front of them. Rolling around my twin bed like a beached whale was no fun but eventually I got the job done.
Just FYI for your DIY!
Also, I have absolutely NO moisture issues. I use a couple of Dri-Z Air units in my van and everything stays nice and dry. It's calcium chloride from concentrated salt water so it's safe to be around. I used the search function and couldn't find anything about them so I'll post about them in the products section.