I used 1/8 stainless mesh to help keep insects (mud dauber wasps, in particular) out, and used stainless safety wire to attach the screens. After installation, I painted the side vents in matching colors. I use 1/8" around here a lot to reduce the impact of flying embers in during wildfires. FWIW: I keep the radiator vent covered with a rodent resistant flap, made from a heavy trunk liner off an older vehicle, mainly just to keep dust and leaves out. (And yes, if someone were to start the generator without removing it, it hovers off in a few seconds, I checked.)
All the best,
2Pbfeet