OK, you can buy one on eBay or Amazon for $10, but I've gone that route and the fit, well, sucked. Plus it can take a while to deliver. I made this in under 45 minutes. I had black art board on hand, but you can use anything ridged that's not metal. Corrugated plastic, heavy cardboard, foam core and so on. As long as the inside is matte black.
Note: I added an update at the end - I made a newer version using formica. You can but scraps dirt cheap, it's thinner than art board and a LOT more durable. Identical steps, but you'll need to cut the formica with a saw, formica cutter, or score and snap (you can find plenty of videos.) Small openings can be cut with a sharp knife or Dremel tool.
First, measure everything. My tablet is just under 8" across, so my back is 8.25". The top and sides can be whatever you want. I made this with a 5" overhang. Cut out the pieces and layout to check it. I cut the "flaps" later on and used scrap from the sides. The back is about 1/4" shorter than the tablet - I want the tablet to clamp in securely, not the shade. The tablet holds the shade in nicely. The shade obviously goes between the mount and tablet.
Angle the sides - I cut 1" off the bottom. Optional.
Grab your best duct-tape. I used a really heavy duty tape from Fiberfix - NOT the black-mesh stuff that dries like fiberglass - this is a really nice duct tape that's nearly impossible to tear. You can also use Gorilla tape, etc. Regular duct tape will dry out over time. Cut it length-wise. So a 2"x8" strip will give you two 1"x8" strips. Scissors will bog down - a knife works best. I stick the duct tape on wax paper then cut it on a cutting board.Stick the strips on one side. Make sure the matte side is in! Many boards have a matte and gloss side. Put the sides in position, folded in, then wrap the tape over. This will leave a slight space between the pieces of cardboard making folding flat easy.
With those spaces the entire thing folds flat! Next I add the flaps - these fold over the outside of the sides and are used to hold it together/open. I used scrap from the top.
For the flaps, put the tape on the inside - you want them to fold the other way.
For my DJI remote, there's a bracket that needs to stick through the shade. Measure twice and cut once. Slice the tape and remove 1/4" from the cardboard. Remove any tape that you slit otherwise it will gum-up your bracket.
I used two large clips to hold the sides down. You can also use binder clips. Originally I was going to use Velcro, but on cardboard it can pull the layers of paper apart. You can see the top of the controller sticking through the top and the tablet in place, the clips holding the sides down.
Test fit on your remote and tablet. Make a mark where you want the cable to go and cut a hole for that. Have the shade ON the remote - don't just put the tablet in the shade and measure. The remote control clamp fits inside the sunshade - so it raises the shade up by the thickness of the clamp.
This will work on a variety of materials. Cardboard is not as durable as plastic, foam core, etc. I did not want to wait for my shade to arrive from eBay, so made this. Good thing - that shade was terrible. Did not fit, flopped around, heavy.
You can also make this from card stock as a test pattern to perfect the fit, then use better materials. Since I had everything on hand, my cost was nothing. Good quality duct tape is around $9 a roll, art board $8 a large sheet. You could probably make 10 shades from one piece of art board.
Step 8: Alternate Material: Formica!
I "enhanced" the build. Originally I was thinking cheap and easy (insert joke of choice here) - I could not think of anything inexpensive and durable that matched art board or foam core. Cut apart a Rubbermaid storage container for plastic sheets? Sure - but too flexible (I've done that in the past.) Sheet metal? Too shiny, a pain to paint, and if you're careless, it's a trip to the E.R. Then I remembered I had a LOT of scrap formica lying around - cut-offs and left overs from previous projects. You can also purchase scrap dirt cheap from many big box stores and cabinet shops. The steps for making it are identical, just double check the location and fir of any openings/slots/holes. These are a pain to enlarge after assembly. Remember to sand all edges and round all corners.