I still think there ought to be an insulated panel of 1"+- which could be placed on existing walls. Even thought it does reduce the interior space, the savings could be greater if it were better insulated.
I am a contractor in California and have a customer with an old 1973 mobile home that leaks and that is not very well insulated. I get cold. He would like to put some insulation and since the outside is already skinned, the work has to be done on the inside. I am looking for a thin panel that can be put on the inside of the home to insulate the walls and ceiling. If you have information not only on the panels, but what distributors exist in central California (between Los Angeles and san Francisco I would appreciate any information you can provide me.