The first thing I do when receiving orders to appraise manufactured home properties is to search the permit history and see if it reasonably coincides with the date of manufacture. As several posters here have confirmed, unless the unit was installed new on the site and not later moved, it is not going FHA or conventional (assuming people are doing their jobs and/or paying attention, which was not the case in the bad old days). I've had a few borrowers tell me during the phone conversation setting the inspection appointment that their unit was moved from a previous set-up; others have informed me when I was doing the inspection. Determining whether it is a new install or a moved unit, and thus whether it can be insured/financed, has always seemed step one to me.
Many municipalities have websites wherein you can search the permit history for properties. If they don't, a call to the planning/building department is the alternative. My experience is if the town is too small to have online records, it's small enough for a staff person to take my call or return it within a day or two with the info. My local online records typically record the site prep inspection, followed by the install date, mechanical, skirting, etc. inspection, then a final. On a recent appraisal, my date of manufacture was 8/6/04, and the dates for permits ran from mid-August through late-September 2004, so it's pretty obvious it was installed new (in this case, confirmed by the borrower who bought it new). Sometimes, a unit sits on a dealer's lot for a year or two, so a bit more research is warranted, especially if the borrower in not the original owner.
Incidently, the MLS description for an active listing next door to the property I reference above stated that the unit had been moved twice, so would have challenges to financing, and sure enough, it has been active for longer than the DOM of most of the comparable sales despite its bargain price. Unless you have a predominantly cash market (ie. retiree buyers), it can definitely impact value.