Here's what can go wrong:
1. You are responsible for lot-rent until the place sells or unless you've got a very desperate park owner. This can Kill your profits if you don't take it into account. My first 'deal' was in a senior park (dumb) and I bought a single for $500. It took me 1 year (at 450 a month) to sell the thing after I spent 1k and numerous weekends fixing it up a bit. I sold for 3k cash as all my buyers were not interested in financing. Oops.
2, If you get over-anxious, you will over pay. It's very easy to rationalize your profits away and work for free. Around here, older DW sell for 25-40k retail. If you can get a place for 20k, you've still got plenty of room for profit right? Lol. I did that and managed a 18% yield on that note. Bought for 18, 2 to fix, 3 to hold, sold for 30k with 3k down at 12%. It's going to take a few years to get my original down payment back there all because I was impatient and failed to negotiate.
3. People don't pay sometimes. When this happens, yes it's not an eviction, but it isn't the cheapest thing in the world to ge the paperwork together for a repo. Luckily, I've not had to do this yet due to a small move out bribe.
4. You HAVE TO be a people person. This is all about shaking hands and listening to stob stories in order to get a decent price. If talking with people and wheeling and dealing isn't your thing, then don't bother.
5. Fires. If your buyer fails to have decent insurance and something BAD happens, you are out your investment as the people who bought it are pretty much judgement proof.
Also to the person who talked about people trashing the place. Yep, that can happen. But, they own they own the place and tend to (thus far) take pretty good care of it. If you were forced to repo a trashed place, it could cost you a little to clear the crap out, but then you just resell WAY cheap and get someone willing to fix the place for you. If it's beyond that, you've lost some money.
Why do it? My best deal thus far is a 82 DW in good condition I bought for 4k and resold in 1 month for 24k with 2.5k down at 12%. I'll have my money back out in around 6 months and will collect a nice payment for years. I've now got around 1.5 a month coming in passively - just xfer the money from one bank account to another from their auto-pays. That's real nice.