A couple of options
One is Velcro screens from underneath which works ok, although the flow coat can peel off the headlining pretty easily where you stick the Velcro. We bought some cheaply ones in a $2 shop in Spain
and cut to suit. Other option is professionally made ones. There's an Aussi company that makes them for about $20 a pop, and I guess other companies do the same. It works ok, you just peel back the corner to open/close the hatch.
The other option is the slide type that have the fly screen
and shade screen
in them. They are great but around $150 each. You might find them cheaper on a RV/ camping car supply site.
Other option is the big net type that fits over the hatch outside and is held down by weights sold in marine
stores. I haven't tried those as they look a bit messy to deal with.