"BTW bob how difficult and expensive was that?"
As always, it depends.
Back then, I had no sewing machine, so I had to sew it all by hand. That takes a lot of time, although it is easy. I think I was able to find some thin mosquito netting that was cheap. You probably want to make it at least 4" high to do any good, but more than 6" might be overkill. Mine was 5", I believe. It is better to have it an inch or two more than you think you need. Otherwise, the bugs will find gaps underneath and make themselves welcome. In fact, if the bugs are really bad some night, pitch it so that an inch or two of the netting is on the ground, and then pile up a few dozen pebbles on it to keep it down.
Later, I had a similar modification on a similar shelter, and I did it by machine.