Some mobile homes are sold on the MLS, but many/most aren't. You already have gotten one posting from someone who'll put it on the MLS for a flat fee. Depending on the price of your home and the amount of work you're willing to do (show it, hold open houses, market it), that may be a good deal. Or you may want a full-service Realtor.
One of the best ways to market a mobile home is to promote it heavily within the mobile home park. Often, the buyer turns out to be someone who already lives there, or a friend/relative/co-worker of someone who lives there.
Hope that helps.