Hi snow0700,
Walmart sells generic 2-piece automotive pop-open sun shades. The "Super Jumbo" plain silver on one side and black on the other, fits the E350/E450 wind shield perfectly. The "Universal" size, fits each van side window nicely. We hold them in place by resting them on the arm rest, then tuck them behind the seat belt upper mount & the edge of the sun visor.
This time of year, Walmart discounts these sunshades. We bought a bunch for $2 per set, gave some to my brother for his E350 motor home, and kept extra for us. They don't last forever. Our first set held up for 6 years.