I made similar window coverings but used a combo of blackout material, Insul-Bright for the middle insulation, and Temptrol to reflect back the sunshine. I like your idea of first glueing and then sewing the magnets inside the pillows. I ended up making "tabs" with polypropylene webbing and sewing the magnets onto that. (Bought the magnets from Apex Magnets on line - the customer service was great at providing the pull forces for the various magnets.) We're still working on the build (plus haven't installed the rear windows yet) so haven't tried them out.