Fleece tends to be quite delicate and can tear very easily. However with a polythene tunnel you are going to have to make sure you water it. I am assuming that your polytunnel is actually a plastic cloche type tunnel, not one you can walk into. If I am wrong let me know.
I would personally stick with the polythene version as you will be more likely to reuse as they will be more resistant to the winter weather.
Hope this is useful