I used one tube the first day, but that was barley enough to have some under the mounts and around the edges, if you zoom in on the picture that was taken after 1 tube and you can see I was only able to get around the edgesof the mount. Another tube and a bit was needed to realy seal up and cover the mounts so no water would pool on them. I also did 6 mounts per panel. I would say if you were doing the standard 4 then two tubes would be good, if 6 like me have three, you don't want to be stingy on the sealant, you also use it to hold the wires in place, so any extra just means you can put a few more blobs to keep the wires secure.