We have used fiberglass and aluminum screen like you find for windows. On the wall fridge vent, sometimes I've hot glued the black fiberglass screen on the back of the vent. You don't notice it and it serves the same purpose as the store bought ones. I've always got the store bought ones for furnace and water heater since they fit so nice. On the bumper, they make caps just to keep bugs out, or you can make your own like some have on here. One spot a lot of people forget about, is the black and gray tank vents and the fridge vent on the roof. On the small black and gray tank vents, I took the cap off (One screw under some sealant), cut an aluminum screen in a circle and fit it on there, and resecured the cap with new sealant. The fridge vent had some screen, but it wasn't a very small mesh so I redid it. I never knew I needed them on the small roof vents until I had dirt dobbers trying to build a nest in the pipe and wall on our Forester. Talk about irritating hearing them and not being able to get them out.
John and Rebecca Dickson
Emma-7 / Little John-5 / Iva-1
Full Timing Again, Rev B
2013 Ford F-350 Lariat CC LB PSD
2015 SOB TT - With OC's Awning Poles (#8)
At least in Heaven, RVs will be perfect, and I won't have to keep fixing them.