I've done it for a single story and the main thing to watch for now is that you have a solid footing/foundation under your mobile home as well as your addition or else your mobile home will move around from ground heave and mess up the whole works and your walls and floors will start detaching and gapping. Of course, all footings/foundations need to be below frost depth for where you live which you failed to mention.
You are really building a 2000 sq.ft. two story house. Ever think about just building you a new house and then selling the trailer? Just thinking out loud for resale purposes.