Off frame "modular homes" are a special breed and are treated just like "stick built" home when it comes to the FHA 203k loan program. We have done several of these and they are quite interesting.
1) How about a mobile home built after June 15th. 1976 on a permanent foundation and affixed to that foundation. The home and site must be under the same ownership and considered "real property". This was an older mobile home... yikes! but were able to use the existing foundation and install new modular home using that foundation and expanding it to fit the new larger home. The new homes are typically larger and require a larger footprint to support the new home. I'll pick up the photos of this one when I get back to Harrisburg. Don't seem to have them on this computer.
2) How about a older SFR on a permanent foundation that is being removed and a new manufactured home will be put in it's place. This one is under construction right now and is coming along nicely. I'll post some photos once we get 'er done.