How difficult are RVs to work on? What makes them so bad?

I've heard over and over, "Don't buy an RV!" They are bad investments. They are often sold using shady practices. The warranties always expire moments before components break. Etc, etc.

I believe all of that and take it to heart. I have no plans to buy an RV.

But one day, I want to buy land and build a house on it, and travel in the meantime, so as an interim form of housing an RV or glamper (camper with all the amenities) seems like a possibly good option.

Therefore I want to know specifically what makes RVs such a no-no from a purchasing standpoint. I'm not afraid of fixing stuff or replacing stuff in a house or in a car--is an RV that much different from either? What's the big problem?

First off, not all RV's are built to the same standards, so some issues come down to luck.

We bought a motor home for trips when the kids were young - so dealing with 4 people. Compared to stopping at a different hotel/motel every night, a motor home was wonderful.

But it wasn't without issues:

1. Noise - *everything* rattled. I learned over time to control what I could by making bags or similar for the things that rattled the most.
2. Some have better levelling mechanisms than others - the fridge didn't work and was damaged if asked to work without decent level.
3. No thermal mass made for significant temperature swings. It got *very* hot in the sun, but it also got very cold overnight if the weather was cold. Some are bound to be better insulated than others.
4. The heater was very noisy and didn't distribute the warmth very well, and it seemed like I got cold within 5 minutes of it turning off. Things like hot water bottles would be a better alternative.
5. Some motorhomes are made for all weather - so the grey water tanks were within the insulation envelope. I recommend that if there's *any* chance you might end up in freezing weather.
6. Humidity - People breath out a *lot* of water and most motor homes don't have a good way to deal with it. Mold is often an issue.
7. Leaks - I've met a couple of motor homes with roof leaks. I would go for a Vardo (Romani) curved roof RV if I was trying to DYI. I refuse to deal with any more flat roofs, unless maybe a stationary green roof - the greenery protects the underlying waterproofing from the temperature/UV extremes that destroy caulking.
8. Poor layout: Most RV's are designed for sunny weather. I rarely see ones with room by the door for gumboots or wet gear. Hanging wet gear in the shower is a common approach, but often you have to cross 6 ft or more of floor to get there. I *have* seem DIY layouts that accepted that rain is a thing and was well designed for it.

Is that enough reasons? If you really want to build a house, may I suggest you build a house on wheels first so you learn lots of skills and get a finished product that will really work for whatever climate you're planning for?

I agree with Jay that not all RVs are the same.

Having owned a variety of RVs and we just bought another one.

We have worked on all of them.  Not much different from working on a house except that the appliances are specific to RVs.

Its not the brand more like RVs require maintenance to keep them in good shape.  Buying one that has not had good maintenance could be a horror story.

Keep dreaming and start looking at RVs to learn about them.  

Instead of an RV, consider a caravan instead.With regard to building, start with a Tiny home as Jay suggested or build a shed to take the caravan when you are on the block.
You then have a protective cover, a rainwater catchment on hand, and you are learning building techniques.
goog luck.

Rumor are rumors. A coworker of mine bought a used Class C RV, drove it to Alaska and back to Indiana ….then sold it for more  than he paid for it.  Sounds like  good investment to me. I wouldn’t buy one , but they might be great for someone else.