The question of weather to finance or not has nothing to do with the OPs question. It's obvious if he was in a position to pay cash the question never would have been asked. :W
When we bought ours the dealer had a better rate than any of the other, normal outlets. Like many, we went 20 years to begin with, but a few years into it rates dropped and we did a refi with Good Sam Credit that shaved 4 years off the note - we kept the payment the same, just shortened the term.
The longer term does let you make a lower payment, but you MUST look at the overall costs. We went 20 years for the lower payment "just in case". Like some others we also make a habit of paying ahead. We paid the MH off in 8 years. We went 20 years on our house, paid that off in 12. I just financed a truck for 5 years, at my current rate it will be paid off well before it's 3rd birthday.
We always figure what the payment would be at a shorter term vs the longer term, normally finance at the longer term but make the larger payment of the shorter term. A longer note gives you the lower payment OPTION as a safety net in case the poop hits the fan and you can't swing the bigger payment. Paying off in the shorter term is normally (always) the better option.