I've done this, both with students and with older folks. Neither group has been particularly more reliable than the other.

Older folks seem stable, but the biggest bind I've been in recently involved a stable, financially-secure professional family whose prime earner got laid off a few days before they were to move in. Sure, I could have taken them to court to enforce our contract....but that's not a pleasant time for anyone, and in the end I would have suffered a loss financially and spiritually for it no matter how the court case went. Plus it would have ruined my trip by making me hang around.

Students seem unstable on the face of it, but the best tenants I've had in a few decades of renting off and on were a group of students. One couple stayed three years, never missing a payment. I charged them somewhat less than market rates, and they were so happy to be getting a deal that they took care of most maintenance on their own, without even letting me know.

I would strongly advise against renting rooms. I've always rented an entire dwelling to specific people, and made them responsible for finding their own housemates. Renting rooms, there will always be someone moving out, therefore the need to interview and vet new people, take fresh deposits, sign contracts, yada yada yada. Does that sound like a carefree holiday to you? Me neither.

Don't forget to set aside money adequate for taxes, maintenance, insurance, emergency repairs, reserves against vacancies of scofflaws, etc. etc. etc. You definitely need some financial reserves in case of any form of difficulty, and you need a reliable local agent (whether professional or not) to handle whatever might come up while you're gone. These people are no easier to find than solid, reliable tenants. Plus you need a plumber, and electrician, a carpenter, and (just in case) a cleaner. Where I come from, if you can't keep the place in "fit for habitation" shape your tenants can legally withhold rent. That means if a window breaks, or the toilet clogs, or the pipes freeze or a circuit burns out, suddenly your traveling money is at risk.

Having said all that, rentals have financed parts of many, many journeys for me. They'll probably finance more trips in the future. It's not as simple as it sometimes seems, and you really need to run through the risks and benefits carefully.

Hope that's helpful.

Mark