Scrounged around in home, office, lab and warehouse tonight and found 36 different kinds of flexible thin plastic films, mostly clear, some black, like trash bags, or white or with colored writing on both sides, everything imaginable really, even shipping tape, etc. Some super thin, like saran wrap, some really thick, like through both sides of a double layer of heavy black garbage bag and double layered plastic grocery bags of all kinds, some still even mildly scrunched up, and everything in between and imaginable, even three different kinds of bubble wrap!
Cranked up FLIR Scout PS, propped up my bare feet as bright white target and proceeded to drape one after another in front of lens. Three different hard plastic sections from product packaging, like what you have to cut with a blade to get into, blacked out the screen, nothing got through them.
Everything else did, some so well I had to double check it was really in front of the lens at all!
When it comes to identifying, selecting, and buying any favorite plastic film in quantity later, I'll also check it out at lower temps, too, not just my 95F feet.
Was above test likely fully valid, as far as comparable results being expected in the field to accomplish mission of OP, too, or might I be missing anything here?
If not, then plastic film covering to keep out wind and air is plenty doable and readily available, especially if best IR transparent plastic, that'll still hold up in environment, does not erode maximum radiating intensity anywhere near as much as air movement likely would have without it there covering apparatus top opening to the black night sky.
Appreciate any comments; good/bad/ugly to enhance goals here, thanks!