To make the serving bowl: slice a small portion of the bottom of the melon so that it will stand. Then cut off the top and scoop out the pulp with a large spoon. (and ice cream spoon works well) Cover rind with plastic wrap and chill.
In a blender or food processor blend the melon, sugar and berries. Remove and press through a fine sieve. Discard the solids.
Add the seltzer and chill. Pour into the chilled rind and serve directly from the melon.
Can add scoops of ice cream or sorbet as an option.