I insulated mine for both road noise and temperature control. My reason for me was sound though. For heat I have a small Mr Ready indoor rated heater and for a/c I have a small portable air conditioner that I can run off of a small portable generator. As of now I'm not worried about conditioned air. My main focus is to get the walls finished up so I can try to figure out what I am going to do to install some sort of a removable bed surface.
On a side note I also picked up a cheap shower rod and shower curtain from Target last week. I have it installed just being the drive/passenger area. It makes a BIG difference in temperature control and noise as well. Definitely worth the $15 it cost.