Many years ago, my father solved this issue by simply building a frame out of 2'x1" timber the full size of the windows, with an upright between each set of louvres. This was laid flat on the verandah, and covered with bronze gauze, tacked on, and then each bit of 2"x1" covered with half round moulding.
The whole lot was held in place by a number of wooden* clips spaced out by lengths of 1" dowel drilled lengthwise with a long screw through them. 
*Not sure of this, may have been short sections of aluminium angle
In our case the set of louvres was about four feet high and about ten feet long. I'm pretty certain that the whole ot was one fitting, but you could do it in more manageable sections. 
The same house had casement windows, and these were fitted with metal gauze 'blinds' on the inside. These were troublesome, but seem to be the only real solution except for a hinged frame opening inwards - this is better if the casement has a wind out mechanism that can be inside the gauze frame.
My flat in Melbourne had the gauze 'blinds', and I wasn't very happy with them either!
				
			 
			
		 
			
				
			
			
				John
JDNSW
1986 110 County 3.9 diesel
1970 2a 109 2.25 petrol
			
			
		 
	
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