I've been freezing red, seedless grapes for years. I buy 10-15 lbs. at a time. I separate the grapes from the stems, place in a large colander, rinse well and then place them in another collander in layers with paper towels in between to absorb all the moisture. I then place them in quart size ziplock freezer bags. It takes a few days for all the grapes in each bag to freeze.
At times I eat them plain but for a real treat, try the following: Place about 1/2 cups worth of frozen grapes in a small bowl and add a couple of teaspoons of plain yogurt, mixing well until all the grapes have a fine coating of yogurt. This keeps the grapes from sticking together. Then add about a teaspoon full of rice pudding and mix again to coat the grapes with a bit of the rice pudding on top of the yogurt. The combination of the grapes with the light coating of yogurt and rice pudding makes a desert that's a treat by themselves, or as a desert after a meal.
When I treat friends to this special treat, they can't believe how great it tastes. They're a treat each and every time. Give it a try,you won't be dissappointed.