I went to Wal Mart yesterday and they had seemingly every different type of Permatext Silicon except the flowable stuff. I did, however, walk out with 2 more Imusa pots and some sporks.
I'll stop by Napa Auto Parts on the way home to see if they have the Permatex. If not then I think the home depot silicone caulk and mineral spirits trick may work.
In addition to my tarp I have 3 rain parkas all of which need seam sealing. My wife found some fairly good rain jackets at Goodwill for $5 each. None of them have pit zips but one in particular has a really nice hood with a mesh liner, inside pockets and velcro cuffs to tighten the sleeves at the wrist Plus, it's large enough to easily fit over a jacket. The material is waterproof but the seams leak. If I can get a good seam seal then I just got a decent rain jacket that only weighs 13 ounces for $5.
BTW, Goodwill has been a boon for us. We found 2 pairs of convertible pants, the kind where the legs zip off to make shorts, both in my size for under $10 each. I found several polypro shirts, both short and long sleeve, for $3 each. And now we have 3 different rain jackets at $5 each. She found herself a puffy down jacket in her size for $15. I would never have thought to check Goodwill but my wife is a pro-shopper and is great at finding deals like this. So be aware, Goodwill is a pretty good source for back country clothing if you don't mind searching through floral pants and old lady blouses to find the good stuff.