I got a roll of reflectix ( or whatever it's called) and cut for the windows of my chev van...made paper templates and cut it out with scissors
for the windshield I got suction cups with hooks in each top corner- I reinforced the reflective surface with tape and used a hole punch for the hook.
for the rear windows which open, I made a little oversize- slid into place & closed window
for the van doors, a little oversize and I hold in place and close the door
a $20 project- home depot