Reflectix, spray-on glue, and this panel:
https://www.lowes.com/pd/Kamo-Panel-...Panel/50113730
Cut the panel into window sized pieces. You can do this with a razor knife. Make them so they fit just inside the side valances and tall enough to slide behind the pull-down shade. For windows with the turning knobs that open the bottom of the window the panels can sit on top of the knobs at the bottom. Other windows that have no knobs will need the Command Wire Hooks (stick-on) to hold the panels up. Cut the reflectix so it is about 1 inch smaller than the panel on all edges. Use the spray-on glue to adhere the reflectix to the plain side of the panel. Let dry, put in your windows and feel the difference.
Also, besides closing the front window curtains, install floor to ceiling thermal panels behind the cab area so that entire area can be closed off. I used 2 of these panels:
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
These curtain carriers:
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
And this track:
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1