RTV Silicone for windows? Where to find?

[gumpy]

I doubt I will be using RTV silicone at this point.  I'm leaning towards the butyl tape, but I am thinking the 3/32" thick stuff I have is not thick enough.

So double it!  Put down two layers of it.

I used the butyl caulk. Yeah, it's a bit messy, till you figure out how to clean it up. Then it's not that bad.
It seals just fine with a proper application. Two thick beads all around the window frame.