That only works out if you can sell your mobile for $50k - typically (there are exceptions based on location and market conditions, but typically) mobile homes depreciate in value, while 'fixed' homes appreciate.
6 years ago if you'd put that $50k down on a 200k house, you'd have had a ~1k mortgage and a home that has appreciated to ~240k, instead of a mobile home that has depreciated.
The trailer home I bought was built in 1984. With all the people moving out of NYC into New Jersey, similar mobile homes in my development have sold for $80k. I may end up selling for a similar amount. Though I do think you're right and it is typical to lose money when re-selling a mobile home.
As a side note: I paid 0 tax when purchasing it (it's not a house, no house tax). My "closing" expenses were $40 to get the title registered at the local DMV / MVC (Motor Vehicle Commission). It's pretty nice.