On older units, buyers often pay cash. Either that, or they use seller financing. The seller might ask for 10%-20% down, with the rest financed over, let's say, 5 years at maybe 12%-14% interest. Problem is, many sellers (just as with conventional real estate) need all their cash in order to move on, and can't do seller financing. One variation (a so-called "Lonnie Deal") used by investors is to buy a home for cash, mark it up, and then sell it on terms. Example: An investor buys a mobile home for $6,000 all cash. He then sells it for $12,000 with owner financing. The seller got what he/she wanted--a cash sale. The new buyer gets what he/she wants--financing. And the investor gets a nice return on investment.
The land lease or lot rent is not deductible. That's property owned by the park, so they're entitled to whatever tax benefits arise from it. However, depending on the state you're in, you do pay personal property tax on the home, just as you would on an automobile. And--check with an accountant--that tax may be deductible. Finally, though you didn't ask, mobile and manufactured homes qualify for the 10% new homebuyer tax credit.