Depending on who's selling the doublewide, you might be able to get owner financing. As you probably know, there are a limited number of lenders even willing to lend on mobile and manufactured homes. Without credit that's acceptable to them, you're often out of luck. Further, the amount you want to borrow is probably much lower than conventional lenders will consider. Where I am, you can get decent double-wides for $30,000-$50,000 and new, gorgeous ones for $115,000. I'm guessing you're probably in the $30,000-$40,000 range. That's below the limit most conventional lenders will lend.
In owner financing, the seller acts as the bank. This is most often successful when the seller is an individual (not a bank or park management). The paperwork's simple, but you should have a lawyer review it. Basically, you'd deal with the seller like the bank: A downpayment, then monthly payments. Sometimes there's a balloon payment at the end; sometimes not. It depends on what you can afford and what the seller needs.
A lease-option, as suggested below, is another possibility. But seller financing is far better for you and, often, the seller. However, the mechanics as described below are inaccurate.
If the seller needs all cash (not uncommon in mobile home parks), another possibility is getting an investor to lend the money. The investor buys the home at a discount for cash. Then he sells it to you on terms. That's the way I'm selling a manufactured home in Virginia right now. I bought at a discount for cash, then am selling to the buyer on terms. I make some money and the buyer is able to buy a home that he otherwise couldn't have.
Hope that helps.