In my 2001 Troll we have a mesh curtain that goes around the whole pop top.
I took my mesh down and out last winter to give it a wash, it shrank slightly , and putting it back was tricky getting it to go behind the toilet screen that hangs down.
It is held up by velcro and it struck me at the time that should I ever replace it , it would be easier to make in one long piece and have a velcro join in it, which could go above the toilet window.
I am not sure that window fly screen as per e-bay, would work very well, better off buying a plainer net curtain, the sort of thing Ikea do.
Highmiler.