Being a cheapskate, rather than replace my van flyscreens when they get a tear, often where they attach to the 'rubber' seal, I use the black windscreen seal compound.
Works very well & matches the rubber seal material.
If it is the permanent ventilation in the top of the sleeve you are talking about, they generally have the mesh sewn on. i suggest you sew a new piece of mesh onto a surrounding and then stick that on with a glue that is used for roll out awning repairs.
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PeterD Nissan Navara D23 diesel auto, Spaceland pop-top Retired radio and electronics technician. NSW Central Coast.
If you just want to stick it on top of a vent a bit of super glue will do the trick
I have magnetic fly screens all around on my house and that is how they stick them to the strips
If you've got a soldering handy you can plastic weld with it. It's not that hard to do, I've done it myself a few times just google "how to plastic weld with a soldering iron" and you get lots of links to Utube videos. A plastic weld will do it better and cleaner than glueing.
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Steve, Di & Ziggy We named our Motorhome "Roadworx" because on the road works "On The Road Again" Ford Transit with 302 Windsor V8 conversion, C4 Auto, 9 Inch Ford Diff All Lighting L.E.D., 260 Amp/h AGM, 530 Watt Solar + Kipor Backup Gen.