Glass containers such as : baby, yoghurt or mustard pots suit. Prefer that which has an insulating lid. You would just have to make a hole in the middle. Avoid metallic lids and replace them by a disc cut for example out a CD case.
Leaves must not be too close to the plate and their surface should correspond almost to half of the surface of this last. When they are parted to the horizontal they must not touch neither be too close to the internal walls of the container. Their mobility plays an essential role in the sensitivity of the electroscope. It is necessary therefore that holes be clean and made nearest to the top in order that leaves do not hinder as soon as they begin to part.
The container has to be clean and dry. I dissuade to wipe it with a paper or a rag. That would have for consequence to deposit charges everywhere. After some manipulations it is easy to remove charges that remain on the glass by rubbing it with a crumpled aluminium leaf.