Not sure about the plastic bag. I would think it could "cook" the pumpkin. My pumpkin plant's leaves usually shade the fruit, so I don't worry about it.

Some of my pumpkin vines trail out into an asphalt alley, so if any of the pumpkins are on the ground there, sometimes I put a Styrofoam meat tray under them, but I'm not sure that is necessary.

I've read here that some people will use nylon panty hoses to keep birds and others away. I haven't done it myself so I don't know much about it.

My main concern are worms boring into the pumpkins.
Would nylons be enough to deter the munching?

Boy I don't know. I did a search of this thread and found this link: http://forums.gardenweb.com/forums/load/gourds/msg081438131023.html
The person said it stopped SVB. Someone else recommended using nylon tulle on the fruit on my old post last year when I was going to do it but ended up just pulling my entire garden up.