The Fuzion line is built very much the same as the Alpine, Avalanche, Raptor and Montana lines (as far as insulation is concerned). There is one member who "did extensive modifications" to his Alpine in an attempt to get it to "winter well"... There are a number of threads regarding his experiences, but here is the "sticky" that he created about his "modifications"...
http://www.keystoneforums.com/forums...ad.php?t=19807
You can also go to this link:
http://www.keystoneforums.com/forums...archid=6623781 and search all of his posts. There is a vast, logical discussion over many threads on the why, where, how of his modifications. Many things, such as his reluctance to use rigid foam sheeting (supports fire and increases the possibility of an underfloor flame spread) and other topics that few consider when they start doing modifications to their RV.
He also attempted to "not use skirting" so that he could remain mobile with his trailer. Once the skirting freezes to the ground, the trailer is essentially "grounded until the thaw".
You may find some helpful hints, considerations and probably a number of things you've not yet considered about winter living in an RV.