Hi there, Sherry. You'll have to use highway 180 to get into the park. I'd then turn south on the General's Highway and try to stay at Lodgepole. You don't say what time of year you'll be there, though. There's a shuttle that takes people to the major trailheads and sights from Lodgepole, but it only runs May to October (not sure what day in October it closes, or if it always runs into October). Website now says "summer shuttle," but I know it was still running last September. At any rate, you can't take a 27 foot RV past the History Museum down to Crystal Cave, and I'm not sure they allow at 27 footer on the road to Crescent Meadow.
But, you can hike to Crescent Meadow from the General Sherman tree, where there is certainly RV parking.
Both Dorst and Lodgepole have RV campsites, but Dorst closes for the winter sometime in October...so the dates are important.
Things open back up again in May - Dorst may not open until mid-June, but Lodgepole will be open.
Not sure I'd go to Kings Canyon with such a short time frame.