Didn’t want mud daubers taking up residence in my furnace vent or water heater enclosure and I didn’t want to spend $45.00 for the form fitted covers so I went to Michaels and found some stuff called WireForm which was on clearance for $2.99 for a 16”x20” piece of screening material. The stuff I got has a 1/8” mesh.

Here is the stuff placed under the furnace vent plate. The furnace is in operation and has been for about 10 minutes when I took the picture. Wanted to make sure the aluminum screening was durable enough.

Here is what it looks like on the water heater vent opening. That one was easiest as the square screen piece put in by the manufacturer just popped out and back in.

Now I just need to figure out a way to screen off the vent by the refrigerator.