Thanks Jay J. I forgot about the all new plumbing, hvac, and electrical systems needed as nothing in the present mobile home can be added on to. You are looking at a whole new hvac system separate from the other and a whole new electrical service drop and main panel. You end up with a whole new piece of real estate attached to a mobile home which will be treated as an added on mobile home. Many places sell them through the car like title instead of a deed. I guess I assumed they owned the real estate and weren't in a park or else it is a definite no no.
Even if you own the land, I would buy a lot, build your 2000 sq.ft. dream home there, put in a deck where you already have the footing and maybe add a garage and then sell the mobile home.
I'd suggest you get ahold of some of your local realtors about the resale issue to see what they recommend and then get you an architect or home builder involved in this major project of yours.
I wouldn't add more than a master bedroom sized room or a garage to a mobile home and even then it would probably need supplemental hvac.