2 cents from a newbie:
*Don't use cheap-o film, go 3m all the way.
*3m also makes an "outdoor" window insulator kit, this tape might hold better in the cold.
*I use 3m on every window, every winter, it's currently 7 below zero outside now. Brrr.
*It's the warmest Tuesday in 3 weeks. Double, no, triple Brrr.
*I don't sleep on this film, but I make pack liners out of it.
*After kids and/or cats have torn my window film, clear box-tape seams to mend it well enough.
*When removing the film, even after many months, it separates from the tape easily; it's designed to be "easily removable".
Here's my thoughts on your tarp idea:
*The ridge-line is the right idea. The tie outs are not.
*Run both sidelines and both A-lines with cord, just like the ridge-line.
*Tie them together; make a self-supporting frame from cordage (1.25mm Z-line? Aka: titanium twine)
*Hem the poly over the cordage as a covering.
*Poly is meant to have a frame to fasten to, not be load bearing.
*Poly will never bond well enough to any tape to bear loads.
*If using a cordage frame, any bonding failure won't be catastrophic.
If you can build an A frame from cord alone, and then hem poly to it, even a charging canine won't tear down the supports, but you still might have a hole in the middle.
Again, just some newbie opinions, so judge me with care lol.