Don't know about how to fix the holes, other than to suggest undoing and redoing the canvas, trying to fit it better.
But, I can wholeheartedly recommend burning a small citronella candle inside when the windows are open.
The screens on my old trailer let mosquitos and black flies through easily. Plus every time the door was opened. We found a small oil lamp at an antique shop and run tiki-torch fuel in it on a very low flame.
We even use the citronella lamp in the new trailer because the door is much larger.
TT 2015 19RD "TheJayco"
TV 2003 F-350 "Montblanc" - Housebroken chore truck
Sitting in The Cheap Seats.
And proud of it!