thanks

You could have the bottom spray foamed with a high quality foam but the roof and mostly the walls and windows will still be very poorly insulated.
I don't think you can make a common trailer like yours or mine supper comfortable during a cold winter.
My in-laws spent the winter in theirs and tried to heat it. It always had hot and cold area's and the windows and even some of the walls were covered condensation. (which promote mold). It was not very nice.
If you really want to do this then I suggest a new, better insulated trailer.