Land Rent: The terms of your land lease agreement will show you your options. You do not want to walk away and then the manufactured home park chases you down and carries you to court.
Home Sale: If you have listed the property with a real estate agent and it has not sold in 5 years then you price is just too high. If the market value is higher than your mortgage, go talk to your lender and see if you qualify for a mortgage relief program. The Obama administration has setup some federal programs that can erase the difference between what you owe and the market value.
Another option is to discuss a short sale with your lender. A short sale grants forgiveness on the excess debt not covered by the sales price.
Another option is to sell the home for whatever you can get and payoff the remaining portion of the loan. It will be cheaper for you (since you move and do not pay lot rent). Plus it will not affect your credit score like a foreclosure.