If your water is all frozen, I mean both hot and cold to all faucets and if you have a compartment that houses all of your connections I would guess that your frozen spot would be right behind that door. If you think about it your plumbing is only 1/2 inch of styrofoam away from -7 degrees.
I know these RV folks say they build a four season unit but most of them recommend you not use it in below freezing conditions.
That being said , if you can determine where it is frozen you can take steps to prevent future problems.
Good Luck