I think mobiles are an excellent investment, there is always someone who can afford to buy them and always someone who can afford to rent them, unlike higer-end homes. My husband and I own several of them (on land) and we love them as investment properties. Mobile/manufactured homes are also about 30% of the single family housing in the united states, and about 40% of the homes in retirement states like AZ and FL.
I used to have license to sell mobile homes that are not on land (in a park where you pay rent) and I let my license go. In my opinion, at least in this area, mobile home parks can be quite a burden and come with a LOT of baggage you wouldn't expect. If you buy a mobile, buy the land underneath it too, don't rent it unless you have thoroughly investigated the park, and their rules and rent increase policies etc. Good Luck!
Many people feel that mobile homes in parks where you own your own land are a better investment. The value of the land obviously will increase.
I agree though, that for some people they are a great way to get your foot in the door, because even if the price of the home goes down a bit (that of course depends on the park, etc.) your home probably will not go down as much in value as the amount you spend each year in rent! Many mobile homes are very lovely and spacious inside! Some of the new ones even have a second story now!
Good luck to you!