Soooo much negativity. Most people are honest, even those who can't get a quick loan on a rapidly depreciating asset.
And situations can cause difficulties getting a loan on a used RV. I know, I couldn't get one in early '16. My credit score is 783, but at the time, no one wanted to loan $50K to a full timing RV'er. I had to pull money out of my retirement acct. Which cost me an extra $8k in punishment money come tax time.
But if I was to consider doing this, I'd certainly go through a service rather than hold the loan myself. Too much trouble when traveling.