they're mostly silicone, no? 3M sells silicone sealant if you really want to go automotive grade, but silicone is silicon, i think. it can withstand a lot of heat. (not talking about pumber's putty)

this is what i have in my bin:

Super Silicone Sealant :3M US

I don't know about the plumbers putty melting. It was always in solid form when we get it from the work truck to use. The trick gets really hot parking out in the sun. Another suggestion would be "thumb gum." That's that green or gray putty that they slap on electrical pipes to keep bugs and water out. That stuff can take the forces of nature face on.

I don't know about the rest of you guys. Sure silicone will work, but will be a pain to rid of with out messing with your paint. Plus I think it stores too solid for the amount of flexing of driving. I think it could make a dent.

JustMy opinion

if you have a thin mouse pad peel the fabric off and cut some washers out of it, mousepads are closed cell neoprene rubber foam, use them to seal milspec connectors.

edit i don't use mousepads but neoprene foam sheeting, but its the same stuff.

Thank you for the suggestions guys. really appreciated! so I just came back from redoing the installation from the scratch, I used 3M tape + weather foam sheet + some silicone sealant. so far so good. I just need to wait silicone to cure and let see what happens when it rains!! :)