For newer RVs much of the cost is spent on appearance and not necessarily functionality. If something breaks on a RV it's not really all that difficult or expensive to repair and/or replace.
A motorhome is going to cost more to maintain than a trailer or 5th wheel because of the engine, drivetrain, wheels, steering, etc. To pull a 5th wheel or trailer you're going to need to maintain a vehicle powerful enough to pull a RV, which is going to add additional costs.
I know people who have been RVing for decades. Some don't travel as they use to and just park their motorhome in a RV park. Once or twice a year drive to their MH paying a monthly fee when at the park and a storage fee when not staying.
You can install wet cell deep cycle batteries where the initial cost is from a few thousand dollars (depending on the size of the bank). If these batteries are regularly maintained, will typically last from 15 to 20 years. Less expensive marine/rv batteries normally won't last as long but are able to last a good amount of time (~10 to ~15 years), when properly maintained.
Similar with other items in a RV. When maintained usually don't break. I know of RVs purchased new in the early 90s that are still going strong. Smaller items such as e.g. a heater fan required replacement.
I find most RVs are easy to work on if you recognize the fact that they're not a permanently grounded structure such as a house or cabin. RV's are built primarily for the road. Some Park models designed to stay in once place, may be an exception, but are essentially the same as regular RVs, unless there is a foundation.
The RV itself (excluding anything required to move a RV, put into motion) most items aren't normally all that difficult to repair. If you want to rebuild or do major repairs on an RV, that's another matter, as often a RV needs to be stripped down, with alot of preparation work.
One example are Epdm roof installations, which require some preparation work, is basically a piece of rubber you cut and fit to the roof. After removing and then re-installing the roof items all that's needed is some caulking. If you do the work yourself, expenses are primarily for the epdm and epdm caulking. Having the work done is another matter. Typical RV labor costs run from around hundred dollars an hour.