(2) Along the seam where the new viscreen ends and the old viscreen was
torn apart, is there a way to "seal" that off?

visQueen aka Vapor barrier.. Yes, use red Tuck Tape to tape the overlap.

http://www.can-save.ca/index.php?opt...95&Item id=93

Make sure you cover it ALL, including where the pipes are..do what you can
with the sheet plastic, then use the tape