the Black Forest is nice but I think it is over hyped a bit - in some ways too romanticized - I would suggest the Mosel Valley as just as nice or nicer a place to motor or rural Bavaria.

i selected black forest because i read a lott about it and am really curious about it.and campervan option came from my husband .he wanna drive so we decided to go for it.
then when i checked it shows many festival but didnt get any information of wine festival happening .(except in spain)

It would be highly unusual for anyone to be having a wine festival in June or July. The previous year's wine is old news and it's months before harvest.

At that time of year you're almost surely going to need reservations for a campervan. People often book a year ahead of time. You'll probably be able to find a spot at the cheap municipal campgrounds, but they will be packed. Do you have experience with driving and setting up a campervan? If not, Europe in mid-summer would not be the place to practice.