Malcolm, I'm the guy what invented the "shower cap" design bug screen for the rear
vanagon door. So here is how to make one real quick and real easy:

Get a sheet of light weight bug screening, large enough to cover the entire rear
opening plus about 2 inches beyond the rubber door seal. With large clothes pegs or
spring clamps attach the sheet of cloth to the rubber seal (with the 2 inches extra).
Adjust the cloth until the wrinkles and folds are removed. Now take a piece of chalk
or dress maker's marker or your kids washable marker pen and mark the screening where
it touches the rubber seal.
Remove the clamps/clothes pegs and the cloth. Cut the cloth at least 2 inches beyond
your marked lines. Fold over a 1/4 inch at the perimeter and machine sew ( to avoid
fraying) and then fold over 3/4 to 1 inch and sew on top on the first stitch.
Get some 1/8 bungy cord about the length necessary to fit all the way around your
screening (less about 2 feet. Take a large safety pin. Attach it to the end of the
bungy cord and insert the safety pin with cord into the 1 inch fold on the screen
perimeter (you'll have to cut a small slit to pass it through) Now work the safety pin
with cord around the entire perimeter until you are back where you started. Tie a good
but small knot in the bungy cord. Slip the knot back into the slot (and stitch up the
small cut)
Now with the help of a friend (or a large clip) fit the "shower cap" over the rubber
door seal until it rests on the metal lip and work the bungy cord around until the
door is covered. It will slip off the first couple of times that you try this.
Now if you want to be able to close the door with the screen in place you will need to
make a hole for the rear hatch lock. The easiest way is to close the hatch, reopen it
and see the hole you have made. Finished.
Larry (not buggy any more)