Foam pad on window in RV door: monofilament holds it in

Yes, Reflectix would work -- this foam pad probably has about the same R-value, but it is stiffer (which helps it stay in place). Reflectix is lighter, which is often a good thing.

I did not want to put velcro on the window, so that is why I went with the fishing line. Plus, the fishing line is just plain funny, and that is always a big plus.