Early German experiments with Bf109 drop tanks

Need a bit of help please with a research project I’m currently involved with. Can anyone point me towards a good source of information about early German attempts to fit the Bf109 with a drop tank? I’m sure I remember reading years ago that they initially tried with ones made from paper mache which leaked (unsurprisingly) so the project was discontinued, only to be brought forward as an urgent operational requirement during the BoB? I think they started to appear in late 1940 and were made of aluminium this time. Grateful for any pointers.