Maxine, I think it varies by specific area. In the Seattle area, street parking is free instead of paid and there's no time limit, except for where the side of the road is required to be clear during a certain time on weekdays due to the bus using it as a bus lane. I use a handicap placard and just go by if the time limit sign is green, and there's no red or yellow signs posted with it, I can park there as long as I need to (up to 3 days, where a different law kicks in.)
Once you get into non-street parking, handicap is not always free. If they're charging everyone else to park there, they get to charge you too, and in almost all cases here in Seattle there's no discount. From what I hear I think other cities have different rules. Wherever you go the information should be clearly posted on signs.
Regarding insufficient room to park an RV in a handicap space, I actually have a suggestion. Assuming it isn't a gigantic class A, calling ahead of time and/or arriving off peak hours and taking up several handicap parking spots before immediately checking with them to get the okay might be a good solution. I've had very good experiences calling up places and being like "Hey! I'd love to shop in your store but I'm disabled and encountering the following access issue. (Describe) I was wondering if there was any chance you might be able to accommodate that?"
Sometimes they say they can't but most of the time they at least try and often really happy that I asked. It helps if you frame things in a simple problem>solution format. "Is there any chance you'd let me take up a few handicap spots to accommodate my disability?" Maybe they'll suggest a different but equally suitable solution, such as coning off two spots pull-through fashion that are right next to the disability spots and thus close enough. Or maybe they'll direct you to park where delivery truck do right outside the store where customers usually can't park. The key thing I've found is for me to suggest one possible solution, and that helps them get a picture of what's needed so they can brainstorm what works best for them. Usually they want disabled people to be able to utilize their services, so as long as it doesn't put them out too much they're happy to do so.
It wouldn't be a hassle-free solution, but if needed I think it would work out just fine.