I would think that other forms of insulation would work better, and look better.
What's a "long time"? Leaving a MH parked for too long without some travel is bad for the coach. Tires will be affected, the fuel can have problems, fuel injection systems can clog, just all sorts of problems.
What kind of ambient temps are we talking about? Most MHs are not designed to live in during long cold weather periods. As you have noticed, they just do not have a lot of insulation. The walls have less space for insulation than the ceiling.
Most people living for extended periods in cold weather take other precautions as well, hay bales work well around the coach to help keep out cold weather and snow. Is the basement heated? How is water supplied to the coach? These are all important considerations in cold weather. How will you refuel, either gas, diesel or propane?
I have assumed your question is directed toward cold weather since we are headed into the cold season.
FMCA #F431170, GS #822128658, Escapees SKP #112655
2012 Airstream Mercedes Interstate Class B