I like the way a 3+ year old post lives on....
So I was at Home Depot and remembered this thread, began to look through plumbing supplies for the plugs, then remembered another product that I thought would do just the trick.
It's called "Protectowrap" and it's a 4" wide rubber membrane used to seal the flashing around windows during home construction. One side is super adhesive, with a plastic peel off sheet to expose the adhesive...I remembered that I had part of a roll left at home from a small remodel/repair job. So headed home, and pulled out the roll, cut off a foot or so, and got prepped to seal up those holes... problem was, the stuff was so old that the plastic wouldn't peel off!
Talked to a home builder buddy of mine this morning...He has tons of the stuff on his jobs, so I'm going to grab some and seal up these holes before I take the 4Runner up to Colorado next month...