Tank vent covers on roof

[Fatdog2]

I was checking my roof A/C and looked at the tank vent covers and found a screw hole filled with silicone sealant that has pulled away inside the hole no longer sealing the hole and screw area. I removed it and replaced one rusty screw and put the vent cover back on. I  used a piece of foam backer rod to fill the deep hole just shy of the top, then filled and overlayed some silicone sealant to seal off the hole.  If you don't seal it, you could have water getting into the interior part of the vent pipe lower mounting ring and inside the camper. It would be a very slow leak, but a leak none the less. I didn't think to take a picture while the cap was off.

[Fatdog2]

I took another picture and better look at the vent covers, and I wanted to put some foam pieces to stop the top of the black water vent pipe from flopping around at the top of the vent cover. As you can see one screw hole base left cover was cracked from the screw driven into to tight. I fixed it with adding a nylon washer and caulking. I replaced the self tapping screws with SS Screws, put backer rod in the majority of hole topped off with silicone caulking.