Here are the rules I have learned to live by with these types of properties.
1. Check to make sure the property has a HUD tag. They are located on the outside as metal clip or under a sink in an older home. If the property does not have a tag your buyer will have to go conventional lending. That will require 20%-30% down.( if you can find one that will do it) otherwise cash sale.
2. If it has a HUD tag the next question is it on a permament foundation? Meaning a basement or tied down below freeze level. ( check with your county requirements)
3. It has to pass an engineniering report for the structure
4. Road agreement.
If the property has all of these it should be able to go FHA. These are the things the lender I use gave me as guidelines to get started on these types of properties. I hope this helps for any one who is unaware of the requirements, to go FHA . It always seems you become educated at the week of closing when the lenders say I am sorry we can not give the loan or you need 30% down and are going to pay a much higher rate. or sorry we can't do the loan it is manufactured not modular
If it does not have a hud tag it will have to go conventional or CASH and well that is not pretty picture. FHA is the best way to take these but it has to meet these requirements.
Country Wide has a program for these type of properties, how ever make sure the lender you use understands the requirements because a lot of them don't and will cause you a ton of headaches .