Not sure how Sadie knows what the plan you are contemplating actually covers, but mindless conjecture is always fun!
Extended Warranties are for those who can afford them and can not or will not fix their own things.
The propensity for catastrophic failure of the vehicle is basically the same as a passenger vehicle of the same age/miles/condition. If you’d buy one for the same age used car, then you have your answer.
If buying for the RV components, there really isn’t a lot to go wrong that is high $ imo. Unless it’s a junker to begin with.
Fridge is the most expensive component, followed by AC, both of which are easy to replace, just costly components.
Slide outs could be a lot of labor. Rest is ticky tack stuff. Hundreds not thousands to fix or replace.