John, did you really use plastic wrap, instead of foil, in the smoker? 
If you must wrap, please use foil next time. You're lucky the wrap didn't melt into the ribs! (Or, maybe it did...you could have confused moistness with melted plastic?).
I know it sounds counterintuitive, but actually, it is common practice in commercial and restaurant kitchens when roasting in the oven to first cover with plastic wrap, then with foil. The plastic must be covered with foil though.
There are a few good reasons for using plastic under foil. One is to get a better seal to hold in moisture. Another is to keep the food from sticking to the foil, like in the case of cheese on a pan of lasagna for example. And a third is to keep the food from reacting with, and pitting the foil. Have you ever seen those little pinholes in the foil, and silver or black specks left on the food? Once again, lasagna is a great example. Or BBQ sauce. Foil can react with salt, acidic, or highly spiced foods. The broken down foil specks are aluminum salts, and apparently do not pose a safety hazard for consumption (even Reynolds wrap states this). Many people use plastic wrap or parchment paper under foil to prevent this.
It seems like the plastic would melt and be an absolute disaster, but it doesn't melt. The moisture under the foil keeps the plastic well below it's melting point. It does seem to get soft, and tear easily, but does not break down. It doesn't even stick to the pan. Most plastic wraps are safe under foil in oven temps up to 375. If you are concerned, you can use food service plastic wrap. I've actually put things covered with plastic wrap in the oven a couple times by accident, and was surprised to find them okay. I think it should be no problem to underwrap the ribs in plastic, especially considering you are at 225-235. I'd like to hear what other forum members who are chefs or have commercial kitchen experience might have to add to the issue.
