It seems to me the issue is better address through parking restrictions. Such as vehicle dimensions, length of time parked, etc. That is if the goal is to keep RVs from tying up parking in certain neighborhoods.
Sleeping opens up can of worms. Some people may find themselves too tired to drive. Forcing one to move on when tired isn't the best policy unless other priorities are more urgent. Sleeping in general is one of the most benign activities a human can engage in. The issues are more a problem with the parked vehicle which should be addressed in other ways.
