It is not constructed to the HUD building code, so it is not a manufactured home. Yes, a manufactured home is always a manufactured home. But if there is no manufactured home left, then it can't be a manufactured home. I would describe it as a site built home, report it on a 1004 and have lots and lots and lots of photos, explanations, describtions, comments, etc, etc, etc. Then let the underwriter figure out how to deal with it. Find building permits from the local authorities, it they are available. Talk to the building inspector, if there is one, ask them which building code was followed while it was being assembled on site. Research, research, research, then explain, explain, explain.