I don't have the operator's instruction anymore, but I thought they cautioned against that. I've always found that my fermwrap is TOO warm as it is, so I usually just have part of it taped on and most of it loose.
I do 5 gallon batches and the coolest by basement gets is 54F in the winter.
I have been using a carboy parka around a fermwrap for a couple years now. I do this inside of a chest freezer and it works very well for lagers and ales. If the ambient temperature is closer to fermentation temperature you can probably leave out the parka.