It depends in part whether you're buying new (or nearly new). In that case, there are some companies that'll lend against mobile homes (and manufactured homes).
If it's more than perhaps 4 or 5 years old, you'll have to come up with other arrangements. Seller financing is a good possibility. Or try to get a personal loan from your bank.
As for terms, that's all negotiable if you can't get one of the big companies to finance you. True story: About 3-1/2 years ago I bought a manufactured home to rehab and resell, offering owner financing. I bought it with cash from the park management. I found a person who wanted to buy it--a good guy who'd had some bad financial issues. I sold it to him with owner financing: 5 years at 11.5%. He contacted me a few weeks ago and asked for the payoff amount. I calculated it and today--really, a couple of hours ago--we met at a bank and he paid it off. It worked out fine for both of us.
The 11.5% interest rate was a bit higher than what some other people were charging. On the other hand, he couldn't qualify for those homes. The 5 year term was fairly typical--it could have been 7 years or so, but the payments at 5 years worked for him.
So, it's all negotiable. But in today's market I'd expect to see interest rates on used mobile homes of 8%-12% and terms of around 5-10 years. Most buyers care more about their total monthly payments than either the rate or term.
Hope that helps.