In reply to Removed UserGRUMPY MONKEY:
There'll be loads of campervans in the parks all summer. You can't sleep in vehicles outside official campgrounds in Yosemite national park, so you may want to book campgrounds in advance - booking opens 5 months beforehand on the 15th of the month, and weekends will sell out immediately. Camping is very nice around there though - most sites have picnic tables and firepits.
There is no problem leaving food in vehicles during the day in car parks in Yosemite NP. In all the campgrounds in Yosemite, you have to take all food out of your vehicle. There's no regulations around Tahoe as far as I know. Here's some more info from the NPS:
https://www.nps.gov/subjects/bears/storingfood.htm